Do the current standards for glucose tolerance testing in pregnancy represent a valid conversion of O'Sullivan's...

The venous plasma values for the 100 gm glucose tolerance test endorsed by the Second International Workshop-Conference on Gestational Diabetes represent an arbitrary conversion from O'Sullivan's original values. The latter were calculated from whole blood by means of the Somogyi-Nelson method. The factor used to convert the whole blood values to plasma glucose values was empirically derived in a population in whom pregnancy status was not stated. A conversion factor derived from a nonpregnant population may systematically overestimate plasma glucose concentration when applied to a pregnant population. Paired specimens obtained from 995 consecutive pregnant patients were analyzed by the Somogyi-Nelson method on whole blood and the glucose oxidase method on plasma. A conversion formula was derived and was used to estimate plasma glucose values and 95% confidence limits equivalent to whole blood values. Application of this formula yields plasma glucose oxidase glucose tolerance test values of fasting, 96 mg/dl; 1 hour, 172 mg/dl; 2 hours, 152 mg/dl, and 3 hours, 131 mg/dl. These values are all lower than those currently endorsed.