The quantitative determination of analytes in body fluids is of great importance in the diagnoses and maintenance of certain physical conditions. For example, lactate, cholesterol and bilirubin should be monitored in certain individuals. In particular, it is important that individuals with diabetes frequently check the glucose level in their body fluids to regulate the glucose intake in their diets. The results of such tests can be used to determine what, if any, insulin or other medication needs to be administered. In one type of blood-glucose testing system, test sensors are used to test a sample of blood.
The test sensor is adapted to receive fluid (e.g., blood) from a user. The test sensor typically includes a base and a lid that is attached to the base. One type of test sensor is an electrochemical test sensor that is adapted to test for an analyte (e.g., glucose). Electrochemical test sensors typically include at least two electrodes to analyze the analyte concentration of the sample. These electrodes of the test sensor are in electrical communication with a meter or instrument that is configured to test for the analyte concentration.
A potential is applied to the electrodes in contact with a biological sample and reagents. The resulting current is measured while the analyte is reacting with the reagents, and then correlated with the amount of an analyte in the sample. Such instruments are referred to as amperometric, in contrast with coulometric instruments that measure the total charge in coulombs produced from reaction of the sample by integrating the current over the entire measurement time. The amperometric instruments are advantageous in that they can use smaller samples and perform quicker tests. Specifically, amperometric instruments do not need to wait for the entire volume of the analyte to be reacted, but rather may take measurements of the analyte by sampling the reaction rate at a predetermined time.
To obtain more accurate measurements, control solutions containing known amounts of glucose are used to verify that the instrument is operating properly. Control solutions have been used that contain blood serum. Some control solutions have been used that replace serum-based control solutions with solutions free of serum, since serum-free solutions are more consistent and stable than those containing serum. Control solutions may contain multiple fixed levels of an analyte concentration (e.g., two or three fixed glucose concentrations) that are formulated to mimic blood serum in terms of fluidity.
Control solutions are used to check the functionality of the analyte monitoring device or meter. Control solutions need to be identified and separated from the readings of real whole blood samples. Specifically, there is a need to automatically detect the control solution by the meter for several reasons. First, the temperature coefficients of the control solution and whole blood may be different. Thus, it is desirable to compensate the temperature effect on glucose readings with separate temperature coefficients. Second, by automatically detecting the control solution and not recording its reading into the memory of real blood-glucose readings assists to provide a more accurate average of blood-glucose readings. Without eliminating the control-solution readings, control solutions will be included in the history of the glucose measurements. Having incorrect historical readings may lead to an incorrect interpretation of a patient's diabetic condition. Additionally, if a control solution is substituted for a whole blood sample, it may be erroneously considered by a physician as indicating a need to change treatment. Third, automatically detecting the control solution and not recording its reading into the memory of blood-glucose readings may minimize the chance of faking the blood-glucose readings by control solution.
Therefore, it would be desirable to have an improved control marker for auto-detection of the control solution and method of using the same.