Decrease in plasma glucose concentration during storage at -20 degrees C.

We measured glucose concentrations with the Beckman Glucose Analyzer, before and after storage at -20 degrees C for various intervals, in 228 plasma samples from oral glucose tolerance tests on 17 normal subjects and 21 patients with impaired carbohydrate tolerance, and also in 82 control samples collected daily, after overnight fast, from seven insulin-dependent diabetics. We found a significantly (p < 0.001) positive relation between storage interval and percentage decrease in glucose concentration. Evidently, the longer plasma is stored, the greater the decrease in glucose.