If you are someone who has to test your blood glucose meter on a regular basis, for diabetes or any other reason, you might assume that your glucose meter is providing you with an accurate reading every time you use it. Diabetics even plan their dose of insulin, diets, and activities based on the number given on a glucose meter. So, how accurate are they? Most glucose meters are designed to give accurate readings of course, but they are not exact measurements. Here’s what you need to know about glucose meters and readings: Accuracy Within 20% If you were to take your glucose reading three or four times in a row, you would probably find you get a slightly different number each time. It isn’t that your glucose meter is functioning improperly, it’s that there is a 20% variance between what a home glucose meter can obtain and the number a lab test can indicate. So, if you get a glucose meter result of 100 mg/dL, it is possible your result is actually 120 mg/dL or 80 mg/dL. A reading within 20% is considered clinically accurate. Home Glucose Meters Measure Blood Different from a Lab When you get your blood glucose measured in the lab, the red blood cells are removed and only the plasma of the blood is measured. A home glucose meter measures all of the blood, including the red blood cells. As a result, the blood sample that includes the red blood cells provide glucose readings that are approximately 12% lower than the lab results from just the plasma portion of the blood. The newer glucose meters have been designed to automatically convert the readings into one that would be closer to that of just a plasma reading like those you would get in the lab. If you don’t have a meter calibrated for plasma blood, then you can do a simple mathematical conversion to compare your home results with a lab result: Divide your lab reading by 1.12. So if you got a reading of 120mg/dL from the lab and you divide it by 1.12, you will get 100 mg/dL. This number is the whole blood (including red blood cells) equivalent of your lab reading so you can compare the number you get on your blood glucose meter with the lab results. Whether your glucose meter is designed to measure whole blood or plasma results, either way you still need to factor in the 20% variance. So a clinically accurate reading will be within 20% up or down from the reading. How to Measure the Accuracy of Your Glucose Meter Right after you have a lab glucose test, use your home glucose meter and compare the result to the lab test to see how accurate it is. (Don’t forget to do the calculation if your home meter is calibrated for whole blood tests rather than plasma results – and if you aren’t sure which reading your meter is providing, call customer service and ask!)