WO1999035487A1

WO1999035487A1 - Methods and apparatus for accurate analysis of bodily fluid constituents

Info

Publication number: WO1999035487A1
Application number: PCT/US1999/000023
Authority: WO
Inventors: John G. Freund
Original assignee: Skyline Venture Partners, L.P.
Priority date: 1998-01-06
Filing date: 1999-01-04
Publication date: 1999-07-15

Abstract

A test strip system and related methods for monitoring analytes contained within bodily fluids such as blood. The test strip includes a substrate member formed with a plurality of reagent sites including a test site and at least one complementary site each within a containment area having reactive reagent material exposed to substantially similar environmental conditions for measuring levels of at least one analyte within separate fluid samples. A closed loop method is further provided for measuring levels of bodily fluid analytes such as glucose wherein a dual site reagent test strip is selected having a first reagent site for a bodily fluid sample and a second reagent site for a reference solution with a predetermined concentration that provides a substantially real-time adjustment value for the analyte level reading of the bodily fluid sample.

Description

METHODS AND APPARATUS FOR ACCURATE ANALYSIS OF BODILY FLUID CONSTITUENTS

FIELD OF THE INVENTION

The present invention relates to apparatus and methods for detecting the concentration or relative amount of biochemical analytes in various bodily fluids. More particularly, this invention includes test strip systems and methods for determining the concentration of blood glucose levels with chemically treated test strips.

BACKGROUND OF THE INVENTION Biological fluids are frequently obtained from patients to determine particular levels of certain biochemical analytes in the course of diagnosis and treatment of diseases. In the treatment of diabetes, it is highly desirable for diabetic patients to frequently monitor their blood glucose levels as a way of helping them maintain near normal blood sugar levels. Medical research has shown that aggressive management of blood sugar levels significantly decreases the long-term complications of diabetes. Blood sugar level monitoring today may include performing multiple blood glucose measurements per day by some patients, particularly those afflicted by Type I diabetes, for guidance in numerous adjustments of multiple injected doses of insulin during each day. Safety precautions and constant monitoring are needed to prevent known adverse medical consequences of diabetes such as morbidity, degeneration of vision or renal failure, and ulcers of the lower extremities which may even progress to a stage where surgical amputation is required.

Although the practice of patient blood glucose measurement will undoubtedly continue in hospital or clinic settings, self-monitoring of blood glucose by diabetic patients at home or in other non-laboratory settings by using "point of care" systems is becoming increasingly important in the management of the disease. As used herein, "point of care" diagnostic systems may be defined as systems suitable for use by the patient when a clinician is not present, even if such systems are sometimes used by clinicians or medical facilities themselves, or when clinicians and patients are present together. From a practical standpoint, it is extremely difficult for non-hospitalized patients to monitor their blood sugar levels with adequate frequency except by performing self-testing. Blood glucose monitoring systems comprising hand-held equipment plus disposable test strips are widely available today to perform blood glucose measurements. These systems often include a portable battery powered electronic device and a mounted disposable reagent-bearing test strip.

During ordinary use, a drop of blood or bodily fluid is applied a single time to the strip so that it reacts with the selected reagents. A colorimetric system may be used to measure a change in the color of a dye resulting from a reaction that is in proportion to the level of the analyte being measured. For example, Fig. 1 -A is an illustration of a photometric blood glucose test strip that is currently available for colorimetric systems. Fig. 1-B is a side view and cross- section of the photometric blood glucose test strip shown in Fig. 1-A. As shown in Figs. 1-A and 1-B, these types of test strips basically consist of a holder 1 formed with an opening or a window 2 on the surface of the holder. A reagent pad 3 is positioned within the holder 1 so that some portion of the reagent pad surface is exposed to a fluid sample through the window 2 of the holder. Alternatively, an analyte level reading may be achieved with an electrochemical system that measures a change in current that is proportional to the amount of analyte being measured. Fig. 2-A, for example, depicts an electrochemical blood glucose test strip that is currently available. Similarly, Fig. 2-B is a side view and cross-section of the electrochemical blood glucose test strip shown in Fig. 2-A. As illustrated in Figs. 2-A and 2-B, the electrochemical test strip also includes a holder 4 formed with a window 5 on the surface of the holder and a recessed wall 7. A reagent pad 6 is positioned within the holder 4 so that some portion of the reagent pad surface is exposed to a fluid sample through the window 5 of the holder. Electrodes 8 are also included in the electrochemical test strip for measuring the blood glucose level of a sample applied to the reagent pad 6. Any of these or other similar types of systems and test strips may provide some concentration level reading or other displayed information for the patient to read. The practice of blood glucose monitoring with test strips typically includes the application of a whole blood sample onto a reagent pad. A reagent pad generally refers to the portion of a test strip where blood or any other fluid may be applied. A whole blood sample is often filtered by a section of the pad to separate serum from other blood components. The separated serum reacts with selected reagents that are typically applied to the pad during the factory manufacturing process. Reagents may include enzymes such as glucose oxidase, horseradish peroxidase, or any other chemically active material used for measuring analyte levels. The applicable chemistry and technology used in colorimetric detection systems provides an end result that is basically an observable change in the color on a reagent pad that is proportional to analyte or glucose concentration levels in a fluid sample. The reaction is typically allowed to occur over a predetermined length of time before the color change on the underside of the test strip is read by a photometer. The photometer translates the magnitude of the color change into analog electronic impulses which may be converted by an appropriate instrument embedded algorithm and displayed digitally on instruments such as LCD displays. Many photometer systems today include an optical light source and a series of focusing elements or lenses, filters and detectors that collectively provide blood glucose level readings.

The disposable test strips in use today often provide a single location or pad on the strip that may contain a variety of reagents. The reagent pad is typically designed to be a site that receives samples of blood or any other bodily fluid. In order to perform a second test, or to test system accuracy using control fluids, the strip is removed and a fresh one mounted before a second drop of blood, control fluid or any other fluid can be applied and measured. When a new package of test strips is opened, a patient typically enters a calibration number into the particular measuring system which is printed on the outside of the strip package or supplied electronically in the strip package. The calibration numbers, which are predetermined and selected during the factory manufacturing process, allow for some system correction resulting from factory variation in the manufacture of test strips. Control fluids with a known glucose concentration range may be purchased which allows a patient to determine whether purchased tests strips or point of care systems are performing within an accepted range or set of specifications established by a system manufacturer. When the glucose concentration of the control fluid falls within the specified range set by a manufacturer for the control fluid, the system and strips are supposedly suitable for use. However, if the control fluid measurement is not within defined parameters or specifications, the patient is directed to exchange the system for a new or repaired one, or to replace the test strips.

Clinicians often encourage their patients to check the accuracy of new test strip packages by sampling the first strip from the package with control fluids after appropriate calibration numbers have been entered. But patients often do not comply with the use of control fluids for various reasons including the constant need to use a test strip from each new package of test strips for testing a control solution. Among other reasons, since most strips used with systems today have a single pad, the control fluid is applied to another fresh test strip which must then be thrown away and cannot be used for a blood measurement.

There are a number of limitations with the above methods and other current methods used to control accuracy in point of care blood glucose measuring systems. Because the systems used today are commonly known to deviate by as much as 15% or more from a correct reading, the system may indicate that it is within specification and suitable for use by the patient if the control fluid is measured to be within 15% of the factory-set concentration of the fluid. Thus, for example, when the control fluid is measured as much as 14% different from the factory-set value, the system still indicates the system is suitable to use. Furthermore, the use of control fluids as practiced today does not account for possible strip-to-strip variability within a package because any indication that the system is performing within specifications applies only to the performance of a single strip or test strip being used with the control fluid. When a fresh test strip is subsequently applied for use with blood, it may or may not have been manufactured at the same time as the strip that was used and tested with the control fluid. Furthermore, the test strips used may or may not have been subjected to the same environmental conditions since they were manufactured. As a result, use of the control fluid with one test strip does not necessarily indicate that any other strip will perform within similar limits. The use of a strip with control fluid again requires the patient to waste another relatively expensive strip, which alone discourages frequent use of control fluids. Because the result from using control fluid only indicates whether a system and strip combination are within specifications, the use of control fluids as practiced today tacitly accepts that each blood glucose measurement may be substantially inaccurate, yet acceptable, so long as the inaccuracy falls within specified limits set by manufacturers. As a result, clinicians often advise diabetic patients that if a measured blood glucose reading deviates from how the patient "feels," the patient should assume the feelings are correct, administer insulin accordingly, and assume that the measurement was erroneous.

Although control fluids and the use of calibration numbers with existing instruments provide some indication as to whether the system is calibrated within certain tolerances pre-set by the manufacturer, they do not correct the measured blood glucose level by employing the difference observed in the measurement of the calibration fluid when compared to the fluid with known glucose concentration. Control fluids used in existing systems may also vary in glucose concentration from factory-set levels when water content in the fluids diminishes due to evaporation while glucose levels remain constant. As a result, control solutions themselves may be inaccurate because their supposedly constant glucose level concentration may actually vary. In any event, a different test strip with potentially different reagent material is often used for measuring the reference solution. There are many reasons for the inconsistent test results provided by current point of care blood glucose measurement systems which may produce readings varying up to 15% or more. When test strips are exposed to humidity after manufacturing, certain enzymes contained in reagent material on the test strip may become deactivated thereby changing the rate at which a measurable reaction can take place. High or low temperatures during storage (such as if the patient should leave packages of strips in the trunk of a car in the hot sun or in extremely cold weather) can also cause deviation in the rate at which selected enzymes catalyze a reaction. A decrease in oxygen levels such as those observed in cities at high altitudes, i.e., Denver, can further cause the enzyme- mediated reaction to be catalyzed at a slower rate. Other non-environmental factors may further cause inaccuracy, such as variations in the manufacturing of the strips, poor technique followed by a patient in the withdrawal of blood samples or its application to the test strip, or drift in the analog portion of the electronics of the instrument.

There is a current need for greater accuracy in point of care blood glucose measurement systems. Diabetics are increasingly encouraged to maintain near normal blood sugar levels for reduction of obvious health risks. For example, patients are especially urged to manage their blood sugar level at bedtime so that it is between approximately 115 and 140 milligrams per deciliter. A reading between this range is recommended so that even if low blood sugar is experienced during the night, it will not be so low that insulin shock or hypoglycemia occurs within the next eight hours or before patients wake up. For example, if a patient measures his or her blood sugar at 100 milligrams per deciliter before going to sleep, a 15% error could mean that the actual blood sugar level is as high as 115, which would be within established guidelines, or as low as 85 which would expose the patient to risk of insulin shock or severe hypoglycemia in the morning. Moreover, existing systems are inconsistent and do not provide readings that are always within 15% of the correct figure. For example, some photometers are within 15% of the correct glucose level only 86% of the time, and other similar products are within 15% of the correct level only 76% of the time. Meanwhile, the American Diabetes Association has stated that self monitoring of blood glucose should be, at all times, within 15% of the results of the reference method. Manufacturers in the industry recognize this problem and attempt to increase the accuracy of their devices as suggested by the American Diabetes Association with complicated devices and procedures. Hospitals frequently use control solutions and more rigorous quality control methodology than is available in point of care systems in order to obtain somewhat more accurate blood glucose measurements that often average within 10%) of accuracy. However, even hospitals do not use control fluids to provide real-time or near real-time correction of the measured blood glucose.

There is a need for a system and method for decreasing the average error to substantially less than 15%, and for increasing the assurance that blood glucose measurement will be within 15%) of the correct figure. Current systems and test strips also fail to provide real-time or near real-time correction of blood glucose measurements. Improvements are needed that satisfy these parameters in order to meet or, more preferably, exceed the current guidelines of the American Diabetes Association in order to provide better blood glucose level management.

SUMMARY OF THE INVENTION

The present invention provides methods and apparatus with the capacity to produce more accurate measurements in monitoring various levels of analytes contained within various bodily fluids. An object of the invention is to provide a system and related methods that accurately measure analyte concentration in bodily fluids such as blood through automatic adjustments within the system to account for variations with the measuring apparatus and chemically active components.

In one embodiment of the invention, a test strip for monitoring a bodily fluid analyte is provided with a substrate member formed with a plurality of reagent sites that includes multiple reagent sites for measuring levels of a particular bodily fluid analyte. Each reagent site includes a containment area with reactive reagent material exposed to substantially similar environmental conditions, but is provided for the analyte level measurement of separate fluid samples. The reagent sites may include a test reagent site and a complementary reagent site for measuring the concentration of the same analyte on the same test strip. Upon application of a reference solution to a complementary reagent site, appropriate adjustments can be made in substantially real-time to correct erroneous analyte level readings derived from the test reagent site. Another embodiment of the present invention provides a test strip for monitoring multiple bodily fluid analytes that includes a set of reagent sites for measuring each bodily fluid analyte. Each reagent site within each analyte set includes substantially similar reagent material within a containment area and is provided for the measurement of a separate fluid sample. In a preferred embodiment of the invention, a blood glucose level monitoring test strip is provided with an individual substrate member formed with dual reagent sites each formed with reagent pads exposed to substantially similar environmental conditions for measuring the level of glucose in a fluid sample. A blood sample may be applied to a test reagent site, and a reference or control fluid with a known glucose concentration may be applied to the other reagent site to provide any needed adjustment factor to the blood glucose level reading. An additional object of the invention is to provide a blood glucose level monitoring kit containing a dual pad dipstick formed with a first test site and a second test site each including a containment area with a reagent treated surface exposed to substantially identical environmental conditions, and a measuring instrument system for determining the concentration of blood glucose test sites on the dual pad dipstick.

It is another object of the present invention to provide monitoring apparatus that includes a spectrophotometric or electrochemical measurement detection system for determining the concentration of a bodily fluid constituent from a test sample, and a dual reagent site strip formed with reactive material within a containment area that is exposed to substantially similar environmental conditions. The apparatus may be suited for various bodily fluids including blood, saliva, urine and interstitial fluid.

It is yet another object of the present invention to provide a method of measuring levels of a bodily fluid analyte with improved accuracy which may include selecting a dual site reagent test strip formed with a first reagent site and a second reagent site each having a containment area with chemically active reagents exposed to substantially similar environmental conditions to measure levels of the same analyte, applying a first bodily fluid sample to the first reagent site to provide an analyte level reading of the first bodily fluid sample, and applying a second fluid sample to the second reagent site to provide an analyte level reading of the second fluid sample. The second fluid sample may be a reference solution with a predetermined concentration of analyte to provide adjustment of the analyte level reading of the first bodily fluid. Alternatively, the second fluid sample may be another bodily fluid sample to provide a separate analyte level reading of the second sample.

Another variation of the invention includes a closed loop method of measuring bodily fluid analyte levels with improved accuracy by selecting a dual site reagent test strip formed with a first reagent site and a second reagent site each with a chemically active reagent exposed to substantially similar environmental conditions to measure levels of the same analyte, applying the sample to the first reagent site to provide an analyte level reading, applying a quantity of the reference solution with a predetermined concentration of analyte to the second reagent site included on the test strip to provide a reference analyte level reading, and adjusting the value of the bodily fluid analyte level reading in substantially real-time based upon the analyte level reading of the reference solution. In yet another variation of this invention, a method is provided for measuring levels of multiple bodily fluid analytes wherein a dual site reagent test strip is selected having at least one set of analyte testing sites which includes a first reagent site and a second reagent site. The bodily fluid may include blood, urine, serum, plasma, interstitial fluid or any other similar fluid.

It is still another object of the present invention to provide a method of manufacturing dual site test strips for monitoring bodily fluid constituents with improved accuracy capacity by selecting a continuous sheet of support material for the test strips, forming at least two set of test site openings along a predetermined path on the continuous sheet of support material for receiving bodily fluid samples, applying reagent material exposed to substantially similar environmental conditions in the proximity to the at least two sets of test site openings formed on the continuous sheet of support material, and forming dual site test strips by selectively separating portions of the continuous sheet of support material and reagent material to provide at least two distinctive sets of test sites on each test strip for improved accuracy capacity. These and other objects and advantages of the present invention will become more apparent from the following description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1-A is a perspective illustration of a photometric blood glucose test strip that is commercially available today.

Fig. 1-B is a side view and cross-section of the photometric blood glucose test strip shown in Fig. 1-A.

Fig. 2-A is a top view illustration of an electrochemical blood glucose test strip that is commercially available today.

Fig. 2-B is a side view and cross-section of the electrochemical blood glucose test strip shown in Fig. 2-A. Fig. 3- A is a perspective view of a spectrophotometric test strip with multiple reagent sites formed in accordance with one aspect of the present invention for measuring bodily fluid analytes with improved accuracy capabilities.

Fig. 3-B is a longitudinal side view and cross-section of another embodiment of the invention that includes at least two reagent sites on a test strip.

Fig. 4 is a top view of another embodiment of the present invention that provides a electrochemical test strip with multiple reagent sites for measuring bodily fluid analytes with improved accuracy capabilities. Fig. 5 is a simplified schematic and side view diagram of a spectrophotometric monitoring system with multiple detectors for measuring levels of bodily fluid analytes within multiple reagent sites on a test strip that is provided in accordance with another aspect of the present invention.

Fig. 6 is a simplified analyte level measuring flow chart and block diagram illustrating various combinations of several analyte level measuring components including sensing apparatus provided in accordance with the invention for spectrophotometric or electrochemical test strips.

Fig. 7 is a simplified sectional view of another embodiment of the invention that provides a test strip for measuring multiple analytes with different analyte test sets for each particular analyte, and multiple reagent sites within each set containing chemically reactive material that is exposed to the substantially similar environmental conditions.

Fig. 8 is a simplified drawing of another aspect of the invention that is directed to a method of manufacturing test strips containing sets of analyte test sites with multiple reagent sites within each set.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It should be understood that the following description of the present invention includes various apparatus and methods for increased accuracy in the monitoring of blood glucose and other bodily fluid analytes or constituents.

Each of these embodiments described below are to be considered individually or in combination with other aspects of the invention.

Fig. 3-A provides an illustration of a spectrophotometric test strip 10 formed in accordance with one aspect of the present invention. The test strip 10 includes multiple reagent sites 11 with two reagent pads 12 for measuring bodily fluid analyte levels wherein each reagent pad is spaced apart and positioned within a separate window or opening 14 in the housing or body 16 of the test strip. The windows 14 in the strip body preferably include tapered edges 15 to assist in the containment of fluid samples when applied to the reagent sites 11. The containment area for each reagent site may of course be formed with other configurations to avoid cross-contamination or exposure between samples within the different reagent sites. Fluid separation between reagent sites may be achieved with or without a physical barrier, and may be formed by simply spacing the reagent sites and pads sufficiently far apart on a substrate member to minimize the possibility of cross-contamination between reagent sites. A single reagent site may of course be divided or separated into smaller distinct sites on the test strip, and alternatively, the reagent sites on the test strip may be separated with perforations such that break away of certain sites may be achieved but not without significant tearing force. The overall test strip housing 16 may be a single continuous substrate member formed of supportive polymer material or any other suitable material that may provide support and fluid control. In addition, the strip body 16 and the reagent sites 11 may be adapted for use with different spectrophotometric systems, and may have different shapes, dimensions and configurations. The strip body 16 may include notches, holes or extensions that are utilized by test strips for various systems available today. The test strip 10 shown in Fig. 3-B also includes two reagent sites 11 on a test strip. A separator element 18 may be formed in the strip body 16 to provide physical support for the test strip 10 and to provide liquid separation between the multiple compartments or sites on the test strip. The test strip 10 may further include a test reagent site and any number or additional complementary sites that are spaced apart and separate to form distinct containment areas.

Each reagent site 11 shown in Figs. 3-A and 3-B includes a chemical reagent pad 12 for reacting with glucose in blood, or any other type of analyte in bodily fluids. The reaction generally provides a measurable color change as an indication of analyte concentration. For example, an analyte such as glucose reacts with reagents such as glucose oxidase to produce hydrogen peroxide. A peroxidase such as horse radish peroxidase, and redox indicators such as o- tolidine, o-dianisdine, 3,3,5,5-tetramethylbenzidine (TMB), 4-aminoantipyrine, and other reagents well known in the art, are capable of being oxidized in the presence of hydrogen peroxide to produce a colored product. The present invention provides test strip apparatus and methods for monitoring analyte levels with these or other chemical reagents that provide measurable color changes, or similar results, with spectrophotometric measurement systems. Chemically reactive material may also be impregnated in the reagent pads at various stages of manufacturing.

The dual reagent sites in the test strips shown in Figs. 3-A and 3-B are provided for measurement of separate fluid samples. Although analyte levels are currently derived from direct placement of bodily fluids samples onto a test strip, the present invention may be modified for non-invasive techniques to include a plurality of reagent sites that monitor or measure analyte levels in samples that do not require the withdrawal of any bodily fluid. The reactive material provided in each reagent site 11 is exposed to substantially similar environmental conditions. The pads 12 and their reagent material preferably originate from the same manufacturing batch. Environmental changes in the post-manufacturing surroundings of the test strip 10 affect both reagents sites 11 , if at all, in substantially the same manner, and to substantially the same extent. At least one complementary site is provided for the measurement of a separate fluid sample such as control solution for calibration of the test strip system. Alternatively, this separate fluid sample may simply be another bodily fluid sample. It should be understood that bodily fluids referred to herein include but are not limited to blood, saliva, urine and interstitial fluid. Each reagent site 11 may also include a membrane covering or mesh 13 for separation of blood components. Hydrophilic meshes are well known in the art, and preferably cover the reagent sites. These coverings or meshes 13 may assist in the separation and measurement of bodily fluid components or analytes. A reagent pad 12 may also include other separation layers (not shown) such as an interference removal layer, a radiation layer, or other types of additional layers that are well known in the art.

Fig. 4 is an illustration of another embodiment of the present invention that includes a electrochemical test strip 20 with multiple reagent sites 21 for measuring bodily fluid analytes. As with other measurement systems, glucose level measurement may be derived from the reaction of glucose with various reagents to produce hydrogen peroxide. In electrochemical systems, an electron mediator such as ferrocene interacts with the hydrogen peroxide to produce a measurable current that is proportional to measured glucose levels. Of course a variety of compatible electron mediators may be used or any other material that will generate current or a measurable result in the presence of hydrogen peroxide.

As show in Fig. 4, the test strip 20 may include two or more reagent sites 21 that contain reagent pads 22 and 29. Windows or openings 24 with tapered edges 25 may be formed in a strip housing or body 26. A first pair of electrodes

27 may be provided in contact with a first reagent site 22, and a second pair of electrodes 28 may contact a second reagent site 29. Additional reagent pads with their respective electrode pairs may be separately provided on a single test strip 20. Each reagent site 21 may be physically separated from other sites by an internal divider 23. In order to provide more accurate readings of different fluid samples, or to minimize the risk of interference between current passing through each pair of electrodes, the internal divider 23 provides separation between reagent pads 22. The reagent pads 22 may be sufficiently spread apart to minimize the risk of fluid samples spilling over to adjacent reagent sites. The test strip 20 may further include a physical division between the reagent sites 21 to maintain the fluid within a controlled containment area.

Another aspect of the present invention provides a method of measuring levels of a bodily fluid analyte with a dual site reagent test strip 10 and 20 as shown in Figs. 3 and 4. Each reagent site 11 and 21 includes a chemically active reagent exposed to substantially similar environmental conditions to measure levels of the same analyte. A first bodily fluid sample may be applied to the first reagent site to provide an analyte level reading of the first bodily fluid sample, and a second fluid sample may be applied to the second reagent site to provide an analyte level reading of the second fluid sample. The second fluid sample may be a reference solution with a predetermined concentration of analyte to provide adjustment of the analyte level reading of the first bodily fluid based upon the analyte level reading of the reference solution. Alternatively, the second fluid sample may be a second bodily fluid sample to provide a separate analyte level reading of the second sample. The existence of complementary sites formed on test strips provide a closed loop method of measuring levels of a bodily fluid analyte with improved accuracy capacity. The present invention provides for bodily fluid analyte level readings in substantially real-time based upon the analyte level reading of the reference solution. Because the reagent sites contain substantially similar reactive material exposed to substantially the same post-manufacturing environmental conditions, the accuracy of level readings may be increased in that upward or downward adjustments to the reading may be derived from a meaningful reference solution reading obtained from a reagent site on the same test strip. As a result, a closed loop system is provided with increased accuracy in real-time or near real-time. The time differential that exists between measuring analyte levels in a test sample and a reference solution may be further considered to provide an even more accurate adjustment value for a level reading.

Another aspect of the present invention is directed to a method of measuring levels of bodily fluid analytes comprising the steps of: selecting a dual site reagent test strip for testing of one or multiple bodily fluid analytes having at least one set of analyte testing sites including a first reagent site and a second reagent site each with a chemically active reagent exposed to substantially similar environmental conditions to measure levels of the same analyte within the same set of testing sites, applying a bodily fluid sample to the first reagent site of the at least one set of analyte testing sites to provide an analyte level reading, selecting a reference solution with a predetermined concentration of analyte, applying a quantity of the reference solution with the predetermined concentration of analyte to the second reagent site of the at least one set of analyte testing sites included on the test strip to provide a reference analyte level reading, and adjusting the bodily fluid analyte level reading in substantially real-time based upon the analyte level reading of the reference solution.

As illustrated by some of the embodiments of the present invention described herein, at least two distinct advantages exist over current point of care systems or other analyte monitoring equipment that are available today. The methods and apparatus provided herein may produce more accurate measurements of bodily fluid analytes such as glucose. For example, fewer temperature adjustment factors are needed for the calculation of test results. As explained above, the reactivity of reagent material in test strips are known to fluctuate as a result of surrounding temperature changes. Analyte level readings also vary from test strip to test strip. Temperature adjustments may be reduced by systems and test strips formed in accordance with the principles of the invention. Similarly, tracking exact batch lots and long term stability of the reagents on the dipstick are less of an issue because the reagent pads on the test strip may originate from the same manufacturing batch in a preferred embodiment of the invention, and are exposed to the same environment conditions which may vary from place to place. For example, various embodiments of the present invention may effectively provide glucose level results that would not vary at high altitudes. The proposed method and apparatus will be less affected by varying altitudes or environment due to the closed system feedback from a control reading on the same test strip in order to provide any necessary adjustments in analyte level readings or values. The advantage of having a test reagent site and at least one complementary reagent site on a single continuous test strip also provides that exposure to moisture and storage temperatures of the dipstick, which are known to affect the reactivity of test strips, have minimal or less of an effect on the test results. An adjustment factor derived from the control reading is provided with this system since reagent pads for either test samples or control solutions are exposed to substantially the same environment after manufacturing. Similarly, lot to lot calibration is not required by the factory or the patient, and no bar code identification is needed on the dipstick to attempt any corrections for variations which will inevitably occur with reference solutions on different test strips. With respect to blood glucose monitoring level systems in particular, more accurate analyte level readings may be further achieved by the addition of a stable colored dye in the glucose control solution which may adjust for any changes in the glucose value of the control solution over time and exposure to climate changes since fluid in the solution may diminish as a result of evaporation. The reference solution may be applied by a patient with a dropper or similar apparatus, or contained within a tiny "bleb" or vial within the strip. The test strip system may further provide for spreading or mixing of suitable chemicals on the strip with those in the control solution so that, after the measurement has been completed, the chemicals used to measure the control solutions and the control solutions themselves are self contained within the test strip. The present invention also provides automatic calibration of an analyte measuring instrument on a measurement-by-measurement basis. This readily provides increased accuracy of glucose or analyte measurements in actual field use, and greater patient and clinician confidence in instrument reading accuracy regardless of the test strip variations and the possibility of "drift" in measurement instrument or test strips due to changes in surrounding temperature, barometric pressure, humidity, instrument and/or strip defects, and the like. The invention may be further useful because, as a result of the automatic calibration on a measurement-by-measurement basis, the system requires less sophisticated or less expensive chemicals than other types of measurement systems that attempt to use more sophisticated or expensive chemicals in an effort to provide more accurate measurements without automatic measurement-by-measurement calibration. For example, the present invention provides for the output derived from a glucose level reading in a control or reference fluid to be fed back into the glucose level reading obtained from the blood sample in order to correct in real-time, or near real-time, the reading obtained for glucose in the blood sample. This provides a reliable point of care glucose measuring instrument and test strip system for home, office, or similar use to measure blood, interstitial fluid, urine, or other bodily substance or fluid. Analyte levels are measured by each chemical strip with multiple reagent sites to perform simultaneous or near-simultaneous readings. One reagent site may be for a blood sample and the other site may be for the reference solution which is used in near real-time to correct the blood glucose measurements. Another advantage offered by the apparatus and methods provided by the present invention is that a test strip may be used more than once. An available reagent site on the same test strip 10 and 20, as shown in Figs. 3-A and B and Fig. 4, may simply provide another test site when analyte level readings are not suspect. This is particularly applicable to patients who frequently monitor analyte levels several times a day. A dual pad dipstick may be used like a single pad dipstick, at lower cost, if the patient decides not to use the glucose control solution and would want to use both pads for measuring two different samples during the day. Other reagent sites provided on the same test strip may be for application of another blood sample for performing two separate blood glucose measurements with the same strip which lowers the cost per blood glucose reading. Even if a patient decides not to use reference solution, blood glucose measurements may be performed with approximately the same accuracy as with instruments on the market today.

As shown in Fig. 5, another embodiment of the present invention includes a spectrophotometric sensing system 30 with multiple detectors 52 and 82 for measuring levels of bodily fluid analytes of samples located within multiple reagent sites 31 and 61 on a single test strip. The spectrophotometer system 30 may include a light source 34 that is supplied with electrical power 32. Multiple light sources may be used to measure analyte levels in different reagent sites on the test strip, or a single light source 34 such as an LED may be used in combination with beam splitting element 33. In order to measure analyte levels in a fluid sample within a first reagent site 31, a portion of light from the light source 34 may be directed with a first mirror 36 or reflective element to a first focusing element 38. Selected portions of light with particular wavelengths may be further propagated through a first filter 40 before reaching a second mirror 42 in the system 30. An incident light ray portion 44 may then be directed towards a first reagent site 31 to produce a reflected light ray portion 46. The reflected light portion 46 may subsequently pass through a second focusing element 48 and a second filter 50 to eventually reach a first optical sensor or detector 52. The portion of light reaching the first optical sensor 52 is detected and converted to an electrical signal 54 for further processing in the system 30. Similarly, analyte levels may be measured at a second reagent site 61 on the test strip by directing light emanating from the light splitter 33 through its respective first mirror 66, first focusing element 68 and filter 70. The light portion may be further propagated towards a second mirror 72 to provide an incident light ray portion 74 that is directed at the reagent pad located at the second site 61. The reflected light portion 76 from the second site 61 may subsequently pass through a second lens 78 and a second filter 80 to reach a second detector 82 which provides a second electrical signal. In this embodiment of the invention, spectrophotometric measurements are obtained for each reagent site 31 and 61 with a single light source 34 and dual detectors 52 and 82. It should be understood that additional light directing and filtering elements may be added to the system 30, or alternatively, the function of the aforementioned components may be performed by common components.

The spectrophotometric measurement system in Fig. 5 may also be alternately configured with a single optical sensor or detector. The light directing and filtering components in the system 30 may be positioned and modified to direct reflected light 46 and 76 to a single detector. The use of a single detector in a preferable measurement system may provide more consistent analyte level readings of samples since different meters with different detectors are known to provide varying readings. Alternatively, the test strip may be repositioned to obtain a spectrophotometric reading of different reagent sites instead of repositioning the measurement components of the system 30. A similar system with multiple measurement componentry may be provided for application with electrochemical test strips in order to obtain readings of current changes in proportion to levels of glucose or analyte levels in multiple reagent sites. In any event, the measurement system 30 may still provide a reading for a test sample or a reference solution in a single reagent site, or multiple readings for samples in multiple reagent sites. The additional reagent sites may be suitable for subsequent test samples or for reference solutions to provide for correction or adjustment factors to test sample readings when necessary. Separate strips with single reagent sites formed from the same manufacturing batch may be used with the measurement system shown in Fig. 5 to correct readings from a test strip sample. Because the reagent material in these sites are exposed to substantially similar post-manufacturing conditions in this closed loop system, readings from the reference solution site on the same test strip provide near real-time feedback and a meaningful adjustment value for test sample readings. A blood glucose monitoring kit is also provided in accordance with the present invention. The kit may include a dual pad dipstick with two reagent sites wherein each site includes a reagent treated surface exposed to substantially identical environmental conditions, and a measuring instrument system as described above for determining the concentration of blood glucose test sites on the dipstick. A reference solution, which may also be included in the kit or otherwise sold separately, may be applied to a reagent site in order to calibrate the blood glucose monitoring system and provide an adjustment value for a test reading. Furthermore, the reference solution may also include a stable colored dye for indicating relative glucose level changes in the reference solution itself. A stable dye may be added to the control fluid to account for any loss of water in the control solution due to evaporation in between the time of manufacturing and the time of use. Although an inaccurate high glucose level would ordinarily result, the stable dye in this system would allow the increased concentration to be measured by the system, and used to correct the accuracy of the reference solution itself.

As shown in Fig. 6, another embodiment of the present invention includes an analyte measurement system 90 that may be adapted for use with different types of test strips for spectrophotometric, electrochemical, or a combination of any other similar type of testing. The system 90, which is shown in a simplified block diagram in Fig. 6, may include various sensing and processing apparatus for both spectrophotometric or electrochemical test strips. A disposable section may be provided in the system 90 for measuring analyte levels of samples on spectrophotometric test strips. The analyte levels in samples contained within the disposable section may be measured by spectrophotometric apparatus that is supplied with a power line for an optical source 92 and further includes a connection for relaying optical sensor signals 94 from the disposable section. Similarly, electrode signals 96 may be obtained from the disposable section when electrochemical test strips are used. Because the temperature of the area surrounding the disposable section may affect the reactivity of the test strip reagents as explained above, the disposable section may also include a heater connected to a heater line 97 and a temperature sensor connected to a temperature sensor line 98. As a result, more consistent and accurate readings may be obtained when the temperature of the reagent sites within the disposable section is kept within a desired range even in colder climates. Other temperature and environmental regulating components may be included in the dual measurement system 90 to compensate for operation in different climates. Because different analog signals of various types may be measured before processing, the system 90 may include an analog/digital interface card. Different measurement signals may be converted to information that may be processed by a digital computing module. The system 90 may of course include a central processing unit or a microprocessor to accept signals relating to analyte level information from the disposable section. Because readings are known to fluctuate over a period of time, a clock may also be used to time the reactions taking place in the reagent sites in the disposable section. When testing a sample or using a reference solution to calibrate the measurement system, appropriate software may be implemented to perform various functions including an algorithm that provides an adjustment value for correcting a test sample reading. Any of this information relating to the disposable section of the system 90 may be further communicated to displays, modems, printers or any other type of output device. At the same time, additional information such as batch or manufacturer information may be entered into the system as operator input to assist in the accurate measurement with different test strips. The invention disclosed herein specifically provides bodily fluid monitoring apparatus for either an electrochemical or spectrophotometric measurement detection system in determining the concentration of a bodily fluid constituent. The measurement detection system may include a electrochemical detector that provides for the relative measurement of the bodily fluid constituent and a reference solution with a previously determined constituent concentration. Similarly, the measurement detection system may be a spectrophotometric detector that provides for testing or the color comparison between a test sample and a reference solution. The concepts of the present invention are equally applicable to each testing system as either single or dual measurement apparatus as explained above.

Fig. 7 is a simplified sectional view of another embodiment of the invention that provides a test strip 100 for measuring multiple analytes which contains different analyte test sets for Analyte A 102, Analyte B 104 and

Analyte C 106. Multiple reagent sites A 108, A' 110 and A" 112 are located within each analyte test set that contains chemically reactive material exposed to substantially similar environmental conditions. The test strip 100 may further provide at least one test reagent site A 108 and one or more complementary reagent sites A' 110 and A" 112 for measuring levels of the same bodily fluid analyte within each set. Each reagent site on the test strip 100 includes reactive reagent material exposed to substantially similar post-manufacturing environmental conditions and is provided for the analyte measurement of separate fluid samples. It should be understood that the test strip 100, and all of the aforementioned test strips, may be formed with as a traditional oblong configuration or any other shape such as a sheet with various lengths and widths of different proportions. The overall test strip 100 may of course simply be a sheet with spaced apart reagent pads placed directly onto the surface of a supportive substrate layer. Fig. 8 illustrates yet another aspect of the present invention that is directed to a method of manufacturing test strips containing multiple sets of analyte test sites for Analyte A and Analyte B. Multiple reagent sites 124 and 126 may provide measurement of different fluid samples for Analyte A. Meanwhile, multiple reagent sites 128, 130 and 132 are provided for different fluid samples of Analyte B. For each tested analyte, a test reagent site A 124 and B 128 is provided for each test strip 122. At least one complementary reagent site A' 126 and B' 130 is also formed on each strip 122. Each tested analyte may include varying numbers of additional reagent sites within each set such as a second complementary site B" 132. The present invention further provides a method of manufacturing these dual or multiple site test strips for monitoring bodily fluid constituents by selecting a continuous sheet of support material 120 for the test strips, forming at least two set of test site openings along a predetermined path on the continuous sheet of support material for receiving bodily fluid samples, applying reagent material exposed to substantially similar environmental conditions in the proximity to the at least two sets of test site openings formed on the continuous sheet of support material, and forming dual site test strips by selectively separating portions of the continuous sheet of support material and reagent material to provide at least two distinctive sets of test sites on each test strip for improved accuracy capacity. The test strips 122 may further be bar coded with an identification number uniquely identifying the batch of reagent material. Although the test strips 122 shown in Fig. 8 are formed with reagent material applied across the entire width of each formed test strip, reagent pads may be positioned within a containment area and spaced apart from the edges of the strip or other pads. While the present invention has been described with reference to the aforementioned applications, this description of the preferred embodiments and methods is not meant to be construed in a limiting sense. It shall be understood that all aspects of the present invention are not limited to the specific depictions, configurations or relative proportions set forth herein which depend upon a variety of conditions and variables including the types of bodily fluids that are monitored or measured, and the use of any combination of the embodiments of the present invention. Various modifications in form and detail of the various embodiments of the disclosed invention, as well as other variations of the present invention, will be apparent to a person skilled in the art upon reference to the present disclosure. It is therefore contemplated that the appended claims shall cover any such modifications or variations of the described embodiments as falling within the true spirit and scope of the present invention.

Claims

What is claimed is:

1. A test strip for monitoring a bodily fluid analyte comprising: a single substrate member formed with a plurality of spaced apart reagent sites including at least one test reagent site and at least one complementary reagent site for measuring levels of the same bodily fluid analyte wherein each reagent site includes a containment area with reactive reagent material exposed to substantially similar environmental conditions for the analyte measurement of separate fluid samples.

2. A test strip for monitoring a bodily fluid analyte comprising: a single substrate member formed with two reagent sites each including chemically reactive material within a containment area that is exposed to substantially similar environmental conditions for measuring levels of a bodily fluid analyte wherein the first reagent site is provided for the measurement of one fluid sample and the second reagent site is provided for the measurement of a second fluid sample.

3. The test strip as recited in claim 2 wherein the reagent sites include chemically impregnated reagent pads that are exposed to the same post- manufacturing environmental surroundings.

4. The test strip as recited in claim 2 wherein the reagent pads originate from the same manufacturing batch.

5. The test strip as recited in claim 2 wherein the second fluid sample provided in the second reagent site includes a control solution for calibration of the test strip system.

6. The test strip as recited in claim 2 wherein the second fluid sample provided in the second reagent site includes another bodily fluid sample for measuring levels of the bodily fluid analyte in the second solution.

7. A test strip for monitoring bodily fluid analytes comprising: a single continuous test strip substrate member for measuring multiple bodily fluid analytes that includes a set of reagent sites for measuring each bodily fluid analyte wherein each reagent site within each analyte set on the substrate member includes substantially similar reagent material within a containment area and is provided for the measurement of a separate fluid sample.

8. A test strip for monitoring bodily fluid analytes comprising: a single substrate member formed with at least one analyte monitoring set of reagent sites including a test reagent site and at least one complementary reagent site for measuring levels of a bodily fluid analyte wherein each reagent site is provided for the measurement of a separate fluid sample within a containment area.

9. A blood glucose level monitoring test strip comprising: an individual substrate member formed with dual reagent sites each formed with reagent pads within a containment area that are exposed to substantially similar environmental conditions for measuring the level of glucose in a fluid sample.

10. The blood glucose level monitoring test strip as recited in claim 9 wherein each reagent site further includes a membrane covering for separation of blood components.

11. The blood glucose level monitoring test strip as recited in claim 9 wherein each reagent site further includes a mesh for separation of blood components.

12. The blood glucose level monitoring test strip as recited in claim 9 wherein each reagent site further includes a chemical reagent for reacting with the glucose in the blood to provide a measurable color change that indicates blood glucose levels.

13. The blood glucose level monitoring test strip as recited in claim 9 wherein each reagent site further includes a chemical reagent for reacting with the glucose in the blood to provide a measurable current that indicates blood glucose levels.

14. A blood glucose level monitoring kit comprising: a dual pad dipstick formed with a first reagent site and a second reagent site each including a containment area with a reagent treated surface exposed to substantially identical environmental conditions; and a measuring instrument system for determining the concentration of blood glucose test sites on the dual pad dipstick.

15. The monitoring kit as recited in claim 14 further including a reference solution for application to a reagent site to calibrate the blood glucose monitoring system wherein the reference solution includes a stable colored dye for indicating relative changes in the level of reference solution glucose.

16. A bodily fluid monitoring apparatus comprising: a measurement detection system for determining the concentration of a bodily fluid constituent from a plurality of reagent sites on at least one test strip wherein each reagent site includes a containment area with reactive material for measuring the level of a body constituent that is exposed to substantially similar environmental conditions.

17. The monitoring apparatus as recited in claim 16 wherein the measurement detection system is a electrochemical detector that provides for the relative measurement of the bodily fluid constituent and a reference solution with a previously determined constituent concentration.

18. The monitoring apparatus as recited in claim 16 wherein measurement detection system is a spectrophotometric detector that provides for color comparison between a test sample and a reference solution.

19. The monitoring apparatus of claim 18 wherein the spectrophotometer detector includes two separate light paths to analyze the sample in each test site.

20. The monitoring apparatus of claims 18 further including a beam splitter to split a single source of light to generate multiple light paths.

21. The monitoring apparatus as recited in claim 16 wherein the bodily fluid is blood.

22. The monitoring apparatus as recited in claim 16 wherein the bodily fluid is saliva.

23. The monitoring apparatus as recited in claim 16 wherein the bodily fluid is urine.

24. The monitoring apparatus as recited in claim 16 wherein the bodily fluid is interstitial fluid.

25. The monitoring apparatus of claim 16 wherein the monitored constituent is glucose.

26. A method of measuring levels of a bodily fluid analyte with improved accuracy capacity comprising the steps of: selecting at least one reagent test strip to provide a first reagent site and a second reagent site wherein each reagent site includes a containment area with a chemically active reagent exposed to substantially similar environmental conditions to measure levels of the same analyte; providing a first bodily fluid sample and applying the first bodily fluid sample to the first reagent site to provide an analyte level reading of the first bodily fluid sample; and providing a second fluid sample and applying the second fluid sample to the second reagent site to provide an analyte level reading of the second fluid sample.

27. The method as recited in claim 26 wherein the second fluid sample is a reference solution with a predetermined concentration of analyte to provide adjustment of the analyte level reading of the first bodily fluid based upon the analyte level reading of the reference solution.

28. The method as recited in claim 26 wherein the second fluid sample is a second bodily fluid sample to provide a separate analyte level reading of the second bodily second sample.

29. A method of measuring levels of bodily fluid analytes with improved accuracy capacity comprising the steps of: selecting a reagent test strip for testing of at least one bodily fluid analyte having at least one set of analyte testing sites including a first reagent site and a second reagent site each with a chemically active reagent exposed to substantially similar environmental conditions within a containment area to measure levels of the same analyte within the same set of testing sites; providing a bodily fluid sample and applying the sample to the first reagent site of the at least one set of analyte testing sites to provide an analyte level reading; selecting a reference solution with a predetermined concentration of analyte; applying a quantity of the reference solution with the predetermined concentration of analyte to the second reagent site of the at least one set of analyte testing sites included on the test strip to provide a reference analyte level reading; and adjusting the bodily fluid analyte level reading in substantially real-time based upon the analyte level reading of the reference solution.

30. A closed loop method of measuring levels of a blood analyte comprising the steps of: selecting a dual site reagent test strip formed with a first reagent site and a second reagent site each with a chemically active reagent exposed to substantially similar environmental conditions within a containment area to measure levels of the same blood analyte; providing a blood sample and applying the sample to the first reagent site to provide a blood analyte level reading; selecting a reference solution with a predetermined concentration of analyte; applying a quantity of the reference solution with the predetermined concentration of analyte to the second reagent site included on the test strip to provide a reference analyte level reading; and adjusting the blood analyte level reading in substantially real-time based upon the analyte level reading of the reference solution.

31. A method of manufacturing dual site test strips for monitoring bodily fluid constituents with improved accuracy capacity comprising the following steps of: selecting a continuous sheet of support material for the test strips; forming at least two set of test site openings along a predetermined path on the continuous sheet of support material for receiving bodily fluid samples; applying reagent material exposed to substantially similar environmental conditions in the proximity to the at least two sets of test site openings formed on the continuous sheet of support material; and forming dual site test strips by selectively separating portions of the continuous sheet of support material and reagent material to provide at least two distinctive sets of test sites on each test strip wherein each test site includes a containment area with reagent material for different fluid samples.

32. The method as recited in claim 31 further including the step of bar coding the test strips with an identification number uniquely identifying the batch of reagent material.