Preservation, distribution, and assay of glucose in blood, with special reference to the newborn

Of several preservatives we tested, a mixture of "isotonic" sodium fluoride and sodium iodoacetate (17.7 and 5.0 g/L, respectively) best inhibits glucose loss from blood collected from the newborn. However, the inhibition is incomplete. Twenty microliters of blood is diluted with 100 microliter of preserving solution. After centrifugation, the glucose in 100 microliter of prewarmed supernate (diluted plasma) is measured in a Beckman Glucose Analyzer, based on the action of a glucose reagent and the rate of oxygen consumption. The method, in effect, determines the glucose in whole blood, except for about 5% of the total that remains in the erythrocytes. Glucose is distributed in blood according to the water content of cells and plasma. From concentrations found in cells and plasma, we can calculate the value for glucose in whole blood with an accuracy of 95.2%. The modified method we describe shows acceptable precision, as judged from within-run and day-to-day CV--generally well below 5% for each.