Blood glucose monitors: What factors affect accuracy?

Sometimes my blood glucose monitor seems to give incorrect readings. What can I do to make sure the measurement is accurate?

Answer From M. Regina Castro, M.D.

When used correctly, blood glucose monitors — small devices that measure and display your blood sugar level — are usually accurate. But occasionally they may be incorrect.

Consider these factors that affect meter accuracy and the steps to resolve or prevent the problem:

Factors that affect accuracy Solutions Test strip problems Throw out damaged or outdated test strips. Store strips in their sealed container; keep them away from moisture and humidity. Be sure the strips are meant for your specific glucose meter. Extreme temperatures Keep your glucose meter and test strips at room temperature. Alcohol, dirt or other substances on your skin Wash and dry your hands and the testing site thoroughly with soap and water before pricking your skin. Don't use hand sanitizer before testing. If using alcohol wipes, let the site completely dry prior to pricking. Monitor problems Fully insert the test strip into the monitor. Replace the monitor batteries as needed. Replace the monitor every 4 to 5 years. Not enough blood applied to the test strip Touch a generous drop of blood to the test strip. Don't add more blood to the test strip after the first drop is applied. Testing site location If you're using a testing site other than your fingertip and you think the reading is wrong, test again using blood from a fingertip. Blood samples from alternate sites aren't as accurate as fingertip samples when your blood sugar level is rising or falling quickly. The amount of red blood cells in your blood If you are dehydrated or your red blood cell count is low (anemia), your test results may be less accurate.

Blood glucose monitor quality control tests

The following quality control tests can assure you that your meter is working properly:

• Test using a control solution. Follow your typical blood-testing procedure, but use a liquid control solution instead of blood. These solutions usually come with your monitor and are available at most drugstores and pharmacies. Follow package directions.

  Use liquid control solutions every time you open a new container of test strips, and then use the solutions occasionally as you use the strips. You generally should also use liquid control solutions if you drop your blood glucose meter, or whenever you get unusual results.

• Match your reading with lab results. Take the blood glucose monitor along when you visit your health care provider or have an appointment for lab work. Check your blood sugar level with your meter at the same time that blood is drawn for lab tests, being sure to use a fingerstick sample, not blood from the blood draw. Then compare your meter's reading with the lab results. Results that are within 15% of the lab reading are considered accurate.

If your meter isn't working properly, contact the manufacturer of your meter and test strips.

With

M. Regina Castro, M.D.

 

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1. Blood glucose monitoring test systems for prescription point-of-care use. U.S. Food and Drug Administration. https://www.fda.gov/regulatory-information/search-fda-guidance-documents/blood-glucose-monitoring-test-systems-prescription-point-care-use. Accessed Nov. 23, 2021.
2. Weinstock RS. Glucose monitoring in the management of nonpregnant adults with diabetes mellitus. https://www.uptodate.com/contents/search. Accessed Nov. 23, 2021.
3. Blood glucose monitoring devices. U.S. Food and Drug Administration. https://www.fda.gov/medical-devices/vitro-diagnostics/blood-glucose-monitoring-devices. Accessed Nov. 23, 2021.
4. Castro MR (expert opinion). Mayo Clinic. Dec. 10, 2021.

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