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October 5, 2000

Blood Tests and Insulin Injections

Question from Sunnyvale, California, USA:

My brother has mental retardation and was diagnosed with diabetes just three months ago. He was using meter "S", but complained about his finger hurting. So we bought meter "F" to test on his arm. The two meters seem to give very different readings at the same time, plus or minus 100 mg/dl�     � [5.6 mmol/L]. Is that normal or am I doing something wrong? What is the difference between plasma-calibrated results and whole blood?


Blood sugar values from whole blood are typically 10-15% lower than plasma values. In addition, blood sugar values between two different meters should not vary significantly — certainly 100 points is far too much variability. Your physician can compare the meters and a sample of blood taken in the office to help sort out which meter is not testing accurately.