Johns Hopkins Diabetes GuideClinical TestsGlucose Monitoring

Hemoglobin A1c

Thomas Donner, M.D., Christopher Saudek, M.D.
Hemoglobin A1c is a topic covered in the Johns Hopkins Diabetes Guide.

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  • Hemoglobin A1c (HbA1c) is a stable adduct of glucose on the beta-chain of hemoglobin (N-[1-deoxyfructosyl]hemoglobin).
  • Formed by a largely irreversible reaction, post-translationally and non-enzymatically, when hemoglobin circulating in a red blood cell is exposed to ambient glucose
  • Alternate terms: "A1c" (preferred for use in communication with patients), "glycated hemoglobin" (the most accurate term), glycosylated hemoglobin.
  • Expressed most often as the percent of hemoglobin that is glycated (alternatively, as mmol glycated hemoglobin per mole total hemoglobin).
  • The single best test to monitor overall blood glucose control in diabetes [6]
  • Reflects the average blood glucose over about 3 months previously, although somewhat disproportionately weighted to recent blood glucose levels [12]
  • A strong indicator of risk for long-term diabetic complications, especially retinopathy, neuropathy and nephropathy (DCCT).
  • Also an indicator of cardiovascular disease (CVD) risk, although glucose control is less strong of a risk factor for CVD than lipids, blood pressure and smoking [8]
  • Recently, HbA1c > 6.5% is recommended as a criterion for diagnosing diabetes [2] [3].

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Last updated: July 31, 2016