Normal Fasting Plasma Glucose Levels and Type 2 Diabetes

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Abstract
Tirosh et al. (Oct. 6 issue)1 found higher fasting glucose levels within the normoglycemic range to be a risk factor for type 2 diabetes in young men. They collected blood in fluoride tubes, which were sent to the laboratory uncentrifuged. However, levels of glucose continue to decrease for up to four hours in fluoride tubes and can drop by variable amounts, sometimes exceeding 9 mg per deciliter.2,3 Most of this decrease occurs in the two hours immediately after venipuncture.2 A change of this magnitude could straddle two of the four top population quintiles described by Tirosh et al. Measurement bias, such as that introduced by failure to separate plasma from cells immediately or by the inherent variability of calibration, limits the use of simple cutoffs for plasma glucose levels in the identification of patients at risk for diabetes. We have suggested methods to minimize errors in venous glucose measurement.4,5