Hemoglobin A1c versus oral glucose tolerance test in postpartum diabetes screening

Abstract

Objective: To determine the usefulness of measuring hemoglobin A(1c) (A1C), alone or combined with the fasting glucose test, compared with the oral glucose tolerance test (OGTT) for the reassessment of the carbohydrate metabolism status in postpartum women with a history of gestational diabetes mellitus (GDM).

Research design and methods: We evaluated the status of carbohydrate metabolism by performing the OGTT and fasting glucose and A1C tests in 231 postpartum women with prior GDM 1 year after delivery.

Results: The prevalence of abnormal carbohydrate metabolism was 45.89% by the OGTT criterion, 19.05% by the A1C test criterion, 38.10% by the fasting glucose test criterion, and 46.75% by the A1C-fasting glucose test criteria. Using the OGTT as the gold standard, abnormal carbohydrate metabolism according to the A1C test criterion had 22.64% sensitivity and 54.55% positive predictive value; abnormal carbohydrate metabolism by the fasting glucose criterion had 83.02% sensitivity and 100% positive predictive value. The A1C-fasting glucose test criteria classified 18 women with normal carbohydrate metabolism as having abnormal carbohydrate metabolism. Abnormal carbohydrate metabolism by the A1C-fasting glucose test criteria had 83.02% sensitivity and 81.48% positive predictive value.

Conclusions: Our results seem to indicate that the A1C test criterion alone or in combination with fasting glucose test criterion does not provide a sensitive and specific diagnosis of abnormal carbohydrate metabolism in women who have had GDM.

Figure 1

Overlap of abnormal carbohydrate metabolism by OGTT criteria and A1C test criteria alone or in combination with fasting glucose criteria. A: OGTT criteria and A1C test criteria (the κ coefficient was 0.070, P = 0.200). B: OGTT and fasting glucose criteria (the κ coefficient was 0.841, P = 0.000). C: OGTT and the combination of A1C test and fasting glucose criteria (the κ coefficient was 0.669, P = 0.000). D: Women classified as having IFG vs. women classified as having IGT (the κ coefficient was 0.141, P = 0.017).