Glucose Readings Looking Off? Here's What Might Have Happened
Nina Ghamrawi, MS, RD, CDE
When used correctly, blood glucose meters are usually accurate. But occasionally or as the meter and strips get older, they may be less correct.
Consider these other factors that affect meter accuracy and the steps to resolve or prevent the problem:
Factors that affect accuracy
Test strip problems
If the test strip bottle is left open, then the strips can become oxidized and may not be as accurate. Exposing strips to moisture may also reduce their accuracy, for example in an insulated lunchbox that also contains food, or in a restroom while showering or near an indoor pool.
Throw out damaged or outdated test strips. Store strips in their sealed container in a dry location that avoids direct sunlight. DO NOT store the test strips in refrigerator. DO NOT combine test strips from different bottles.
When you open them, write the date that you opened them on the bottle of strips. They will expire after 5 months and need to be thrown out.
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 before pricking your skin.
If you have typically sweaty or clammy hands, or they are freshly washed, your glucose reading may also be diluted and read artificially lower.
Poor circulation, or "milking the finger"
If you have typically poor circulation, you may need to massage, or "milk" the finger to get enough blood. If over-massaged, your finger can leak some interstitial fluid into the blood, resulting in an artificially low reading.
Some meters must be coded for use with each new bottle of test strips. Our meter doesn't require this and should be more accurate from this perspective.
Not enough blood applied to the test strip
Touch a generous drop of blood to the test strip. DO NOT add more blood to the test strip after the first drop is applied. Sometimes a lot of blood may come out of your finger, but if it is smeared by the test strip first, then the test strip may not gather enough of a sample. This can cause a fake low reading.
To make sure the blood is applied correctly to the test strip, make sure your blood sample is a nice round drop, and put the center tip of the test strip at the very edge of the blood drop.
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.
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 and artificially high.
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 normal blood-testing procedure, but use a liquid control solution instead of blood. Follow package directions. Only use the control solution provided by the meter’s manufacturer. Use liquid control solutions every time you open a new container of test strips, and occasionally as you use them. You generally should also use liquid control solutions if you drop your blood glucose meter, or whenever you get unusual results. For iHealth meter's control solution, you can contact your care team to get more information.
Match your reading with lab results. Take the blood glucose meter along when you visit your doctor 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. Then compare your meter's reading with the lab results. Results that are within 15 percent of the lab reading are considered accurate.
If your meter isn't working properly, contact your Care Team in the Unified Care app or give us a call. We are trained in helping you resolve these issues.