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A1c’s May Not Reflect Postpartum Glucose

Jul 28, 2011

In women with recent gestational diabetes, alignment of A1c with glucose levels is only “fair”….

Dr. Catherine Kim of the University of Michigan, Ann Arbor states that, “A1c tests are easy to use after delivery for a diabetes screening test, but clinicians should be aware that they do not match up well with glucose in this time period when iron stores tend to be low and women’s hemoglobin levels are in flux.” 

In a July 12th online paper in Diabetes Care, she and her colleagues report on 54 women with histories of gestational diabetes who were reassessed between 6 weeks and 36 months postpartum.

An A1c at or above 5.7% had 65% sensitivity and 68% specificity for identifying women with either a fasting plasma glucose level of at least 100 mg/dL, or a two-hour glucose of at least 140 mg/dL. For identifying elevated FPG alone, A1c had 75% sensitivity and 62% specificity.

A1c, the researchers note, does not require fasting or glucose loading, so it could improve postpartum testing rates. However, “Use of glucose would presumably lead to more diabetes diagnoses.”

Dr. Kim added that “correlations between hemoglobin A1c and glucose levels from an oral glucose tolerance test are low at 6 weeks after delivery and improve at 1 year after delivery.”

To determine the optimal test, she and her colleagues conclude, “outcome-based studies are needed.”

Diabetes Care July 12, 2011.