Fasting plasma glucose as a diagnostic indicator of diabetes mellitus

Among 233 patients referred for glucose tolerance test (GTT), 36.4% of 129 non-pregnant subjects were classified as diabetic, compared with only 2.9% of 104 pregnant subjects. Preliminary screening using a fasting plasma glucose upper cut-off of 7.0 mmol/l, above which the subject was classified as diabetic and a lower one of 4.4 mmol/l, below which he or she was considered normal, would have eliminated the need for 30% of GTTs and positively identified 60% of the diabetics in the non-pregnant group. Only one patient would have been significantly misclassified, possibly owing to inadequate fasting. However, little benefit would result from applying an upper cut-off to low-prevalence populations such as the pregnant group. Like other recent surveys, this study suggests that World Health Organisation diagnostic figures for fasting plasma glucose could be revised downwards to 7.0 mmol/l. Conversely, to be fairly certain that an individual is not diabetic, fasting plasma glucose must be below about 4.4 mmol/l.