Mayo Clinic Health Library

Question

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?

Updated: 03-13-2012

Answer

When used correctly, blood glucose monitors — small devices that measure and display your blood sugar level — are usually accurate. But occasionally they're 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Test strip problems Throw out damaged or outdated test strips.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 heat, 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 your hands and the testing site with soap and water before pricking your skin.
Improper coding Some meters must be coded to each container of test strips. Be sure the code number in the device matches the code number on the test strip container.
Monitor problems Fully insert the test strip into the monitor. Replace the monitor batteries as needed.
Not enough blood applied to the test strip Apply 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 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.

Blood glucose monitor quality control tests

When you start a new container of test strips, occasionally perform these quality control tests as you use them and when your results seem unusual.

To perform a quality control test, do one or both of the following:

  • Test using a control solution. Follow your normal 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.
  • Match your reading with lab results. Take the blood glucose monitor along when you visit your doctor or have an appointment for lab work. Check your blood glucose with your meter at the same time that blood is drawn for lab tests. Then compare your meter's reading with the lab results. Your meter's result is considered accurate if it falls within 15 percent of the lab test result.

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