If you have taken your blood sugar twice or three times in a row without any delay in between tests, then you have probably noticed that you don't get the same exact number each time. That does not mean your meter is not operating correctly, but it does, though reflect the variance that is built in to each meter.
Within the medical community, home glucose meters are clinically accurate if the result is with in 20% of what a lab test indicates. For example, if your glucose meter result was 100 mg/dl, then it could vary on a downside to 80 mg/dl or on the up side to 120 mg/dl and still be considered clinically accurate.
Y0ur glucose meters measures blood differently than a lab.
All blood glucose meters use whole blood to measure glucose. Whole blood is simply a blood sample that contains the red blood cells. In a lab glucose test, only the plasma portion of the blood is used to measure glucose levels, so the red blood cells are removed. Whole blood glucose tests are app. 12 percent lower than the plasma results. But, there is a way to compare the lab results with your meter. Before you do that, you should know your meter.