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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


Donner, Thomas, and Christopher Saudek. "Hemoglobin A1c." Johns Hopkins Diabetes Guide, 2016. Johns Hopkins Guide, www.hopkinsguides.com/hopkins/view/Johns_Hopkins_Diabetes_Guide/547062/all/Hemoglobin_A1c.
Donner T, Saudek C. Hemoglobin A1c. Johns Hopkins Diabetes Guide. 2016. https://www.hopkinsguides.com/hopkins/view/Johns_Hopkins_Diabetes_Guide/547062/all/Hemoglobin_A1c. Accessed July 18, 2019.
Donner, T., & Saudek, C. (2016). Hemoglobin A1c. In Johns Hopkins Diabetes Guide. Available from https://www.hopkinsguides.com/hopkins/view/Johns_Hopkins_Diabetes_Guide/547062/all/Hemoglobin_A1c
Donner T, Saudek C. Hemoglobin A1c [Internet]. In: Johns Hopkins Diabetes Guide. ; 2016. [cited 2019 July 18]. Available from: https://www.hopkinsguides.com/hopkins/view/Johns_Hopkins_Diabetes_Guide/547062/all/Hemoglobin_A1c.
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TY - ELEC T1 - Hemoglobin A1c ID - 547062 A1 - Donner,Thomas,M.D. AU - Saudek,Christopher,M.D. Y1 - 2016/07/31/ BT - Johns Hopkins Diabetes Guide UR - https://www.hopkinsguides.com/hopkins/view/Johns_Hopkins_Diabetes_Guide/547062/all/Hemoglobin_A1c DB - Johns Hopkins Guide DP - Unbound Medicine ER -