What is the role of hemoglobin A1c (HbA1c) testing in the diagnosis of diabetes?

Updated: May 10, 2021
  • Author: Jiun-Lih Jerry Lin, MBBS, MS(Orth); Chief Editor: Eric B Staros, MD  more...
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In conjunction with glucose tolerance testing (GTT), another useful indicator for the diagnosis and monitoring of diabetes mellitus includes hemoglobin A1c (HbA1c) testing. HbA1c is glycated hemoglobin. Its value, measured in percentage of all hemoglobin, is used as an indicator of the serum glucose value over the last 3-4 months. The American Diabetes Association considers an HbA1c value of greater than 6.5% to be diagnostic of diabetes mellitus, and a value of 5.7-6.4% to be associated with a high risk for developing diabetes. [4]

A retrospective study by Poon et al indicated that in pediatric patients with overweight or obesity, a combination of HbA1c and alanine transaminase levels, as well as family history of type 2 diabetes mellitus, can be used to predict which children should undergo oral GTT. The investigators reported that there was a 61.6% positive predictive value for an abnormal GTT when the HbA1c was 5.5% or above, the family history was positive for type 2 diabetes, and the serum ALT level was abnormal. [5]

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