To establish more reliable criteria for the diagnosis of hypoglycemia during fasting, studies of plasma glucose concentrations during 72 hours of fasting were conducted independently at two institutions. Premenopausal women did not stabilize glucose at a level comparable to men. Twenty-four subjects, both men and women, were fasted in Study I. The mean (± S.E.M.) lowest glucose recorded was 66.4 ± 2.9 mg per 100 ml in men of normal weight and 47.8 ± 2.9 mg per 100 ml in women. In Study II the mean lowest glucose in 40 fasts by women was 41.3 ± 1.9 mg per 100 ml. No variation was noted in the early and late phases of the menstrual cycle. Three prepubertal children had glucose responses during fasting comparable to those of women.

To be considered abnormal, plasma glucose must decrease in women to less than 35 mg per 100 ml within 24 hours, and in men,55 mg per 100 ml. After 36 hours of fasting, it is virtually impossible to judge the diagnostic implications of plasma or blood glucose values in premenopausal women. (N Engl J Med 291:1275–1278, 1974)