There are a number of instances when it is desirable or necessary to test or monitor the concentration of an analyte, such as glucose, lactate, or oxygen, for example, in bodily fluid of a body. Bodily sample analyte tests are routinely conducted in a variety of medical settings (e.g., doctor's office, clinic, hospital, by medical personnel) and in the home by the patient and/or a caretaker. For example, it may be desirable to monitor high or low levels of glucose in blood or other bodily fluid that may be detrimental to a human. In a healthy human, the concentration of glucose in the blood is maintained between about 0.8 and about 1.2 mg/mL by a variety of hormones, such as insulin and glucagons, for example. If the blood glucose level is raised above its normal level, hyperglycemia develops and attendant symptoms may result. If the blood glucose concentration falls below its normal level, hypoglycemia develops and attendant symptoms, such as neurological and other symptoms, may result. Both hyperglycemia and hypoglycemia may result in death if untreated. Maintaining blood glucose at an appropriate concentration is thus a desirable or necessary part of treating a person who is physiologically unable to do so unaided, such as a person who is afflicted with diabetes mellitus.
The most important factor for reducing diabetes-associated complications is the maintenance of an appropriate level of glucose in the blood stream. The maintenance of the appropriate level of glucose in the blood stream may prevent and even reverse some of the effects of diabetes. Certain compounds may be administered to increase or decrease the concentration of blood glucose in a body. By way of example, insulin can be administered to a person in a variety of ways, such as through injection, for example, to decrease that person's blood glucose concentration. Further by way of example, glucose may be administered to a person in a variety of ways, such as directly, through injection or administration of an intravenous solution, for example, or indirectly, through ingestion of certain foods or drinks, for example, to increase that person's blood glucose level.
Regardless of the type of adjustment used, it is typically desirable or necessary to determine a person's blood glucose concentration before making an appropriate adjustment. Typically, blood glucose concentration is monitored by a person or sometimes by a physician using an in vitro test that requires a blood sample. The blood sample may be obtained by withdrawing blood by lancing a portion of his or her skin, using a lancing device, for example, to make blood available external to the skin, to obtain the necessary sample volume for in vitro testing. The fresh blood sample is then applied to an in vitro sensor, such as an analyte test strip, which is positioned in a meter or the like, whereupon suitable detection methods, such as calorimetric, electrochemical, or photometric detection methods, for example, may be used to determine the person's actual blood glucose level.
Available self-monitoring analyte systems generally include an analyte meter having a receptacle for receiving a cartridge containing a plurality of disposable analyte testing devices, e.g., test strips, which are individually and automatically dispensed on demand. An analyte test strip includes one or more chemical reagents designed to interact with a target analyte(s) in body fluid applied to it in such a way that an analyte meter connected to electrodes of the test strip can derive a value of the level of the target analyte contained in the body fluid. The meter may be an integrated device which provides a lancing function in addition to measuring the level of target analyte(s) in the body fluid being tested. Where the analyte test strips provide only a test component, the lancing is performed by a separate lancing mechanism housed within the meter. In other systems, the test strip may be integrated with a lancet into a single component, such as disclosed in U.S. patent application Ser. No. 12/488,181, herein incorporated by reference in its entirety. In either variation, the meter is configured to dispense the testing devices from the cartridge one at a time, as needed.
The test strip cartridge may include a biasing member at a loading end of the cartridge to bias the contained test strips towards the cartridge's strip-dispensing end. A seal is typically provided at the cartridge's strip-dispensing end for minimizing exposure of the test strips within the cartridge to ambient air. The seal is typically made of an elastomeric material configured to be released temporarily to permit loading of a test strip from the cartridge to within the meter for the lancing and testing processes. A desiccating material may be provided separately within the cartridge or integrated into the structural support of the cartridge to help maintain the analyte test devices substantially free of moisture. An advantage of an automatic test strip cartridge is that numerous analyte tests may be performed without having to manually load a new test strip for each test performed.
Examples of integrated lancing and testing systems are described in U.S. patent application Ser. Nos. 10/629,348, 10/701,993, 10/837,886, 10/899,773, 11/035,131, 11/146,897, 11/160,407, 11/160,427, 11/350,398, 11/535,985, 11/535,986, 11/830,760, 11/830,770, 11/830,779, 11/830,786, 11/831,649, 11/831,706, 11/868,762, 11/870,420 and 12/035,348, the disclosures of which are herein incorporated by reference.
Due to certain lot-to-lot inconsistencies in the test strip fabrication and manufacturing process, there may be variations in test strip sensitivity between lots which require some form of system calibration for each batch of strips. Currently, existing calibration mechanisms require the use of a calibration strip by the user, the inputting of a calibration code by the user, or the use of a machine readable mechanism on the strip or cartridge to modify the reaction interpretation of the meters for a particular lot of test strips.
Despite means for calibrating meters for given test strip lots, if a test strip is past its expiration date or its chemistry has otherwise degraded due to humidity and other constituents of the ambient atmosphere to which it has been exposed subsequent to fabrication and packaging and prior to actual use, i.e., during the test strip's shelf-life, unpredictable and unreliable analyte test results are likely. Moreover, during actual active use of a test strip cartridge, the cartridge is opened and closed by the meter each time a test strip is used, exposing the remaining test strips to an even higher level of ambient air, thereby contributing to degradation of the strips, even in the presence of a desiccating material within the cartridge.