Limitations of A1c Interpretation

Jessica G. Shepard, PharmD; Anita Airee, PharmD, BCPS; Andrew W. Dake, MD; M. Shawn McFarland, PharmD; Amit Vora, MD


South Med J. 2015;108(12):724-729. 

In This Article


Evaluation of hemoglobin A1c levels has become the standard of care in the management of diabetes mellitus. Currently, the ADA recommends checking A1c levels every 6 months in people with well-controlled diabetes mellitus and every 3 months in people with uncontrolled diabetes mellitus or if recent medication changes were made. Given the importance of A1c in diabetic care in the prevention of retinopathy and nephropathy and in long-term studies of myocardial infarction and the movement toward pay-for-performance models, it is paramount for healthcare providers to understand the limitations of A1c testing.[60–62]

Hemoglobin A1c is a reflection of average blood glucose in 2 to 3 months, but it provides no information on the degree of daily blood glucose fluctuations. As such, healthcare providers should continue using self-monitoring blood glucose (SMBG) results to evaluate glycemic fluctuation as well (Table). When comparing A1c and SMBG, one must consider variable eating habits, glucometer reliability and interactions, patient technique, hypoglycemia, and postprandial hyperglycemia.[10] Because there is no single reference standard for control of diabetes mellitus in any given patient, optimum treatment of the patient would involve the integration of symptoms, SMBG, and various tests of average glucose control to evaluate the patient.

Many factors exist that may affect a patient's A1c. When A1c and SMBG results do not correlate, it is especially important to consider these patient-specific factors. The 2015 ADA Standards of Care state that discrepancies between a patient's A1c and SMBG levels should warrant exploration of the reasons for these discrepancies. Considerations should include testing method, hemoglobinopathies, conditions affecting red blood cell turnover, chemically modified hemoglobin, altered rates of glycation, race, and age. If a healthcare provider decides A1c is unreliable in a particular patient, alternative strategies for assessment of glycemic control should include more frequent or different timing of SMBG and continued glucose monitoring, as recommended by the ADA. In addition, clinicians can consider evaluation of fructosamine, glycolated albumin, and 1,5-AG; however, there are no consensus guidelines for their use.