Blood Glucose Meters
The accuracy of your test results depends partly on the quality of your blood glucose meter and test strips and your training. Other factors can also make a difference in the accuracy of your results.
Hematocrit. Hematocrit is the amount of red blood cells in the blood. Patients with higher hematocrit values will usually test lower for blood glucose than patients with normal hematocrit. Patients with lower hematocrit values will test higher. If you know that you have abnormal hematocrit values you should discuss its possible effect on glucose testing (and A1C testing) with your health care provider. Anemia and Sickle Cell Anemia are two conditions that affect hematocrit values.
Other Substances. Many other substances may interfere with your testing process. These include uric acid (a natural substance in the body that can be more concentrated in some people with diabetes), glutathione (an "anti-oxidant" also called "GSH"), and ascorbic acid (vitamin C). You should check the package insert for each blood glucose meter to find what substances might affect its testing accuracy, and discuss your concerns with your health care provider.
Altitude, Temperature, and Humidity. Altitude, room temperature, and humidity can cause unpredictable effects on glucose results. Check the blood glucose meter and test strip package insert for information on these issues. Store and handle the blood glucose meter and test strips according to the instructions.
Third-Party Test Strips. Third-party or "generic glucose reagent strips" are test strips developed as a less expensive option than the strips that the manufacturer intended the blood glucose meter to be used with. They are typically developed by copying the original strips.
Although these strips may work on the meter listed on the package, they could look like strips used for other blood glucose meters. Be sure the test strip you use is compatible with your blood glucose meter.
Sometimes manufacturers change their blood glucose meters and their test strips. These changes are not always communicated to the third-party strip manufacturers. This can make third-party strips incompatible with your blood glucose meter without your knowledge. Differences can involve the amount, type or concentration of the chemicals (called "reagents") on the test strip, or the actual size and shape of the strip itself. Blood glucose meters are sensitive to these features of test strips and may not work well or consistently if they are not correct for a blood glucose meter. If you are unsure whether or not a certain test strip will work with your blood glucose meter, contact the manufacturer of your blood glucose meter.
Performance Goals for Blood Glucose Meters
Deciding performance standards for blood glucose meters has been controversial and challenging. In spite of efforts in the late 1970s and 1980s by both FDA and CDC, no universally accepted standards or testing methods have been developed for the measurement of glucose. The CDC (Centers for Disease Control and Prevention) recently held a standards conference and is exploring the possibility of developing a standard reference material for whole blood.
The ADA has recommended accuracy goals twice over the past twenty years, once in 1986 (target accuracy of +/- 15%) and once in 1993 (target accuracy of +/- 5%) No company that manufacturers glucose meters has developed a cost-effective system to meet these goals. A number of alternative standards have been suggested by national standards organizations in the U.S., Canada, and Europe. An international standard ISO DIS 15197 is currently under development that recommends accuracy of +/- 20 mg/dl (1.11 mmol/l) for glucose values under 100 mg/dl (5.56 mmol/l) and +/- 20% for higher glucose values.
Although data on blood glucose meters continue to show variable performance, the newest generations of blood glucose meters are simpler to use and more accurate than older models. Improvements in the chemical, mechanical, and software components of blood glucose meters are continuing to help with the management of diabetes.
1-American Diabetes Association. Standards of Medical Care in Diabetes - 2010. http://care.diabetesjournals.org/content/33/Supplement_1/S11.full. (Accessed 7/5/11).
2-FDA. Glucose Testing Devices. http://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/InVitroDiagnostics/GlucoseTestingDevices/default.htm. (Accessed 7/5/11).
Reviewed by Francine Kaufman, MD. 4/08
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