ReviewImplications of Using Hemoglobin A1C for Diagnosing Diabetes Mellitus
Section snippets
Evolution of Diagnostic Criteria for Diabetes
The first widely accepted laboratory standard for diagnosing diabetes was proposed by the World Health Organization (WHO) in 1965.8 It stated that the disease was present if a venous whole-blood glucose concentration was ≥130 mg/dL (plasma glucose ≥150 mg/dL) 2 hours after a 50- or 100-gram oral glucose challenge.
In 1979, the National Diabetes Data Group proposed new diagnostic criteria.9 These were based on the midpoints of bimodal curves observed in certain populations tested for FPG and for
Correlation With Microvascular Complications
A1C is accepted as the best single measure of average glucose concentration,16, 17 and it is used routinely to guide adjustments to therapy. A1C has been shown to correlate with likelihood of diabetic retinopathy,18, 19, 20 and in some studies this correlation was found to be stronger than that for fasting glucose.19 In large clinical trials of both type 1 and type 2 diabetes, A1C also correlates with the probability of developing other microvascular complications.21, 22
Technical Considerations
With the adoption of the
Who Gets the Diagnosis of Diabetes: A1C ≥6.5% Compared to FPG ≥126 And 2-Hour PG ≥200?
The ADA report on the new diagnostic criteria states that based on data from the NHANES, the A1C cut-point of ≥6.5% will identify one-third fewer individuals than a FPG cut-point of ≥126 mg/dL.1 Other studies confirm this viewpoint. A report comparing the 1999 WHO criteria (2-hour PG) and the 2003 ADA criterion of FPG ≥126 mg/dL with an A1C of ≥6.5% found that A1C categorized the fewest individuals as having diabetes.38 A1C identified 5.2% of individuals in this study as diabetic, compared to
Special Considerations that Apply to the AIC Assay
Multiple factors affect the accuracy of the A1C as an indicator of average glucose concentration (Table 2). Appropriate use of the A1C for diabetes diagnosis requires that clinicians be aware of these factors. For comparison, some factors that affect glucose concentration are listed in Table 3.
When using A1C as a diagnostic tool, it is important that the test be performed in a laboratory that uses a method certified by the NGSP. This program allows clinical laboratories to relate their A1C
Conclusions and Recommendations
The A1C obtained from appropriately selected patients and performed in a qualified laboratory provides an accurate measure of the individual's mean glucose concentration. It correlates well with the probability of microvascular complications, and it offers significant technical and practical advantages over laboratory glucose measurement. There are confounding factors (Table 2) that can interfere with A1C assay accuracy, and clinicians need to be aware of these. The ADA diagnostic threshold of
Acknowledgment
The authors thank David Harlan, MD, for his critical reading of the manuscript.
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2019, Primary Care - Clinics in Office PracticeCitation Excerpt :There are many ways that the hemoglobin A1C measurement may be prone to error. Point-of-care machines for hemoglobin A1C, which are being used more widely, open the possibility for occasional unreliable results.46 There are also ethnic variations in hemoglobin A1c testing, with African Americans being more prone to false-positive tests and white persons prone to more false-negative tests.47,48
Diagnostic Criteria for Prediabetes
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Funding: Supported in part by Center Grant DK32520 from the National Institutes of Health and by grant 7-08-RA-106 from the American Diabetes Association (Dr. Mordes). The contents of this publication are solely the responsibility of the authors and do not necessarily represent the official views of the National Institutes of Health.
Conflict of Interest: All authors declare that there are no conflicts of interest.
Authorship: All authors had access to the data and a role in writing the manuscript.