Chemistry: molecular biology and microbiology – Measuring or testing process involving enzymes or... – Involving glucose or galactose
Reexamination Certificate
1998-06-25
2003-02-11
Gitomer, Ralph (Department: 1627)
Chemistry: molecular biology and microbiology
Measuring or testing process involving enzymes or...
Involving glucose or galactose
Reexamination Certificate
active
06518034
ABSTRACT:
1. FIELD OF THE INVENTION
The present invention relates generally to blood glucose testing. In particular, the present invention advances a testing method and apparatus for use in determining blood glucose concentrations.
2. BACKGROUND OF THE INVENTION
The fast and accurate determination of one's blood glucose level is crucial to those with diabetes, especially for individuals who are insulin dependent. Failure to monitor blood glucose levels frequently and adequately can lead to severe health problems, diabetic coma, and, in some cases, death.
Given the importance of monitoring blood glucose levels, the prior art includes devices for self-monitoring. Self-monitoring permits diabetic patients to measure their own glucose level in a non-laboratory setting and at relatively low cost. Thus, self-monitoring improves the ability of diabetics, including those who have busy schedules and who travel frequently, to regulate their blood glucose levels.
The most prevalent form of self-monitoring employs a “test strip” and a photometer. A “test strip” is a substrate material that carries a reagent. The reagent is a chemical composition containing one or more chromophores that react chemically upon exposure to the analyte of interest, in this instance, glucose. When exposed to glucose present in blood plasma, the chromophores change color, with the degree of color change being a function of the glucose concentration.
A conventional photometer is a hand-held electronic device that measures the quantity of light reflected from a particular body. The reflected light measured by the photometer translates by programming into a glucose concentration value using reference data that relates glucose concentration as function of reflectance for a particular chromophore. The photometer also displays the glucose level in mg/dL using a liquid crystal display or light-emitting diode.
In use, a patient will place a small sample of his blood on a defined area of a test strip containing the reagent composition. Typically, the individual will be required to wait a predetermined number of seconds before removing excess blood from the surface of the test strip.
The test strip is then inserted into the photometer. After another predetermined period of time, the photometer will display the results of the glucose measurement. More recent systems do not require the user to wipe excess blood and thus are called “non-wipe” systems.
Other “non-wipe” self monitoring systems measure blood glucose levels as a function of electrical resistance rather than color change of a reagent. In these systems, a “Wheatstone bridge” is utilized instead of a photometer. A Wheatstone bridge is a four-arm bridge circuit which measures an unknown electrical resistance, which in this instance is the resistance of the blood glucose which varies with concentration. In use, an individual places a quantity of blood onto an impermeable substrate and in doing so, completes the bridge circuit.
Despite the fact that non-wipe systems are superior to their predecessors in both accuracy and convenience, present day non-wipe systems do not consistently yield results that are as accurate as clinical measurements. Although the American Diabetes Association has stated that self-monitoring systems should produce readings within 15% of the actual glucose level, present day self-monitoring systems fall short of that level of accuracy. Self-monitoring systems fail to yield consistently accurate results for several reasons, including variation in the thickness of the reagent composition, inhomogeneity of the reagent composition, insufficient oxygen for driving the reaction between the reagent composition and the blood, poor separation of red blood cells from plasma, and thermal degradation of the enzymes within the reagent composition during the bonding of the reagent to the substrate.
Thus, there exists a need for a blood glucose testing method and apparatus that is inexpensive and easy to use but consistently yields clinically accurate glucose concentration values.
SUMMARY OF THE INVENTION
According to its major aspects and briefly stated, the present invention is a testing method and apparatus, including test strip and photometer for use in measuring the concentration of blood glucose levels. The test strip comprises a substrate to which is adhered a polymeric membrane having a quantity of reagent composition applied on the side of the membrane opposite the side that is adhered to the substrate. The arrangement of the elements of the test strip is very important. The polymeric membrane, preferably a polyethersulfone or acetate membrane having a porosity between approximately 250 and 1200 microns, is centered on an aperture formed in the substrate. Double-sided tape is used to adhere both the membrane and the reinforcing layer to the substrate.
The photometer of the present invention uses infrared light to determine blood glucose. The amount of light reflected by the reacted components from the drop of blood on the test strip is converted to a blood glucose value and displayed. Additionally, the meter has built-in tests to determine if the reaction has failed to go to completion or the value determined is outside the nominal range of the meter. In addition, the meter has a number of features to make it easier to use.
A droplet of blood is placed in the aperture of the substrate and, when its plasma has migrated through the membrane and reacted with the reagent, infrared light is directed to the reagent side of the membrane for reflectance analysis. The substrate is preferably made of polyvinyl chloride in a neutral white or light gray color that preserves the integrity of the photometry and occludes stray light, and provides structural support to the membrane.
The reagent composition is applied only to the surface of the polymeric membrane and then heated to a temperature no greater than 129° F. for an exposure period of time of no longer than 20 minutes to adhere the reagent composition to the surface of the membrane, rather than allow it to soak into the membrane. Reagent-free pores in the membrane enable them to perform a mechanical separation of plasma from red blood cells that would otherwise adversely affect a photometric analysis based on reflectance of red or infrared light. Keeping the pores substantially free of reagent also enables them to deliver the oxygen needed for the reaction between blood glucose and the reagent.
Accordingly, a major feature of the present invention is the specific location of the membrane placed on the substrate. The membrane is placed between the substrate and the reagent. When a sample of blood is deposited on the top of the membrane through the aperture in the substrate, the size of the membrane pores traps the red blood cells but enables the plasma to migrate through the membrane. As a consequence, the blood which contacts and subsequently reacts with the reagent is relatively free of red blood cells. Filtering red blood cells from the blood sample prior to contact with the reagent minimizes the occurrence of incomplete reactions or reaction gradients, which in turn results in more accurate blood glucose readings.
In addition, the surface of the membrane is air permeable and therefore permits air to contact the reagent composition. This air, and oxygen in particular, serves to drive the reaction between the blood and the reagent composition to completion, and thus maximizes the accuracy of the resulting blood glucose reading.
Another major feature of the present invention is the use of infrared light to detect the changes in the reagent when it has been exposed to the blood components. A non-visible type of light minimizes the influence of visible light in the photometry but, only when red blood cells have been separated from the glucose component of the plasma can infrared light be practical to use.
Other features and advantages will be apparent to those skilled in the art from a careful reading of the Detailed Description of a Preferred Embodiment accompanied by the following drawings.
REFERENCES:
patent:
Cole Gilbert W
Phillips Kevin J
ABB Diagnostics, Ltd.
Gitomer Ralph
Mann Michael A
Nexsen Pruet Jacobs & Pollard LLC
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