Distinguishing test types through spectral analysis

Details Distinguishing test types through spectral analysis Distinguishing test types through spectral analysis

2001-02-28

2003-05-13

Snay, Jeffrey (Department: 1743)

Chemistry: analytical and immunological testing

Automated chemical analysis

Utilizing a moving indicator strip or tape

C436S063000, C436S067000, C436S164000, C422S082050, C422S082090

Reexamination Certificate

active

06562625

ABSTRACT:

DESCRIPTION OF THE INVENTION
1. Field of the Invention
The present invention relates generally to methods and apparatus for determining the test type to be performed on various types of test elements. More particularly, this invention provides methods for distinguishing between different types of test elements, including analytical test strips with fluid samples applied to them, analytical test strips with control solution applied to them, and standard strips as measured by a reflectance-type testing device.
2. Background of the Invention
Monitoring analytes such as glucose, cholesterol, intoxicants, and other constituents is frequently desirable in fluids, such as blood, plasma, blood serum, saliva, urine, and other biological fluids. In healthcare applications, such monitoring affords the opportunity to make rapid diagnoses of a patient's condition and to take prophylactic or therapeutic measures necessary for maintaining proper health.
One such healthcare application that has benefited tremendously by analyte monitoring in recent years is the treatment of diabetes. Diabetics suffer from an impaired ability to regulate glucose levels in their blood. As a result, diabetics can have abnormally high blood sugar levels known as hyperglycemia. Chronic hyperglycemia may lead to long-term complications such as cardiovascular disease and degeneration of the kidneys, retinas, blood vessels and the nervous system. To minimize the risk of such long term complications, diabetics must strictly monitor and manage their blood glucose levels.
Diabetics that have glucose levels that fluctuate several times throughout the day require very close blood glucose level monitoring. Close monitoring of blood glucose levels is most easily obtained when a diabetic is able to monitor their glucose levels themselves. Many devices currently available allow diabetics to measure their own blood sugar levels.
Reflectance-based monitors comprise one category of personal, or home-use, glucose level monitoring devices. These monitors utilize an optical block which accepts test elements for photometric analysis.
The test elements are usually in the form of test strips, which contain analytical chemistry. Conventionally, these test strips are in the form of a disposable diagnostic test strip containing analytical chemistry upon which a fluid sample is deposited. Once the user applies the fluid sample to the test strip, and the sample has sufficiently penetrated the test strip, a chemical reaction occurs in the presence of a target analyte, e.g., glucose, to cause a change in the optical properties of the test strip. An optical photometric device then determines the analyte level of the sample by measuring an optical property, such as the intensity of reflected light at a certain wavelength from the test strip. For in vitro analysis in healthcare applications, the fluid sample is usually fresh whole blood. Periodically, however, it is desirable to run a test on a test element formed by applying a control solution of known analyte concentration to a test strip, in order to verify that the meter is performing within operational limits. It is also desirable for the user to insert a “standard strip”, which is a test element that has known optical properties, in order to verify that the meter is operating within operational limits.
Diagnostic test strips for testing analytes such as glucose levels of blood samples are well known in the art and comprise various structures and materials. Test strips typically include single or multi-layered porous membrane arrangements which receive a blood sample and undergo a change in an optical property, such as a color change, in response to the interaction of blood glucose with agents/reactants in the membrane. Examples of such multi-layer strips are described in U.S. Pat. Nos. 5,296,192 to Carroll and 6,010,999 to Carroll et al., the contents of both of which are incorporated herein by reference.
Prior to reaching the reactants, a whole blood sample can be filtered to eliminate potential optical interference by removing erythrocytes, or red blood cells. Some test strips operate to allow the applied blood sample to migrate to a reaction site in the membrane where the sample reacts with the agents/reactants, which is located in downstream capillary relation to the sample application site. The results of the reaction are often visible as a color change at the reaction site. However, the change may occur in invisible regions of the electromagnetic spectrum, such as infrared and ultraviolet. For the purposes of this application, the term “color change” will be understood to include variations in optical properties throughout the visible and invisible regions of the electromagnetic spectrum. As noted above, a color change can be correlated to the amount of glucose in the sample. Home-use glucose measuring devices that use a reflectance meter to measure the color change of the test strip correlate glucose levels to the change in the amount of light reflected from the reaction site of the test strip. As is well known in the art, strips can be formulated to produce a color change within a certain spectral region, and the meter designed to photometrically measure reflected, absorbed or transmitted light at a wavelength sensitive to the color change of the strip. While the present invention will be described with reference to reflectance based photometry, it would be known to one having ordinary skill in the art to apply the features of the invention to absorbance or transmittance based systems.
Desirable for maintaining the accuracy of blood glucose monitoring devices is the periodic checking of the device to ensure that it is within operational compliance. As mentioned above, certain periodic standardization tests performed by the user provide verification of the meter's accurate operation. Accuracy is required by regulatory authorities for medical devices such as diabetes testing monitors, where a patient's life can depend on proper operation of the monitoring system.
Common verification techniques are designed to periodically check whether the monitoring device is operating properly, and thus accurately measuring blood glucose levels. Verification techniques used in glucose level monitoring devices include inserting test elements having a known glucose or reflectance value into the monitoring unit and comparing the measured results with the known values. Test elements having known glucose levels (“Control Test Elements” hereinafter) are normally prepared by applying a glucose control solution having a known glucose concentration to a dry test strip that normally could be used to run a test with blood. The control test element is then inserted into the monitoring unit and a test is performed and the calculated glucose value of the test element is displayed. The calculated glucose value is then compared with a range of acceptable results provided by the manufacturer for the glucose control solution. If the results displayed by the device for the control test element fall with an acceptable range designated for the solution, the device is deemed to be appropriately functioning ready for testing a blood sample.
Another verification technique commonly used in glucose level monitoring devices includes inserting a strip with a known reflectance value into the monitoring unit (“Standard Test Element” of “Standard Strip” hereinafter). This standard test element does not receive a fluid sample, but is rather formed of a one piece rigid or semi-rigid material such as plastic having known optical properties. The standard reflectance strip can be stored in a compartment of the monitoring unit so that it is conveniently available for use throughout the life of the monitoring device. The standard reflectance strip is inserted into and measured by the device just as other test strips, and the measurement results are compared with a range of acceptable results provided with standard reflectance strip. As with the test using the glucose control test element, if the results of the measurem

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