What are limitations of HbA1c testing in the diagnosis of diabetes mellitus (DM)?

Updated: Oct 23, 2019
  • Author: Romesh Khardori, MD, PhD, FACP; Chief Editor: George T Griffing, MD  more...
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Answer

HbA1c testing cannot be used in patients with abnormal red cell turnover (eg, hemolytic or iron-deficiency anemia). [1]

The American Association of Clinical Endocrinologists recommends that HbA1C be considered an additional, optional diagnostic criterion, rather than the primary criterion for diagnosis of diabetes. [106] Using HbA1c alone in initial diabetes screening identifies approximately 20% fewer cases of diabetes than diagnosis based on fasting and 2-hour postload plasma glucose levels. [112]

Moreover, a study presented in 2019, using data derived from 9000 adults, reported diabetes diagnosis with the HbA1c blood test to be unreliable. The investigators found evidence that in comparison with the OGTT, HbA1c testing would lead to a 42% overdiagnosis of glucose tolerance and a 73% underdiagnosis of diabetes, in adults. [113]

Glucose measurement should remain the choice for diagnosing pregnant women or if HbA1c assay is unavailable. In addition, a study by Nowicka et al stated that used on its own, HbA1c is not effective in detecting prediabetes and diabetes in obese children and adolescents. [114]


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