The American Diabetes Association (ADA) has approved evidence-based guidelines for the use of hemoglobin A1c (HbA1c) in the diagnosis and management of diabetes, and a recent study has shown that the test is an effective tool for identifying prediabetes when used in combination with impaired glucose fasting.

The recommendations, compiled by an expert committee to supplement ADA guidelines, state that HbA1c may be used for the diagnosis of diabetes, with values ≥6.5% being diagnostic (Diabetes Care. 2011;34:1419-1423).

Point-of-care HbA1c assays are not sufficiently accurate for the diagnosis of diabetes. An HbA1c testing method certified by the National Glycohemoglobin Standardization Program should be performed in an accredited laboratory. Factors that interfere or adversely affect the assay will preclude its use in diagnosis, just as they would preclude its use in management of the disease.

HbA1c values that are inconsistent with the patient’s clinical presentation should be investigated further, advised the authors.

The guidelines also clarify the role of HbA1c testing once the person has been diagnosed with diabetes. Treatment goals should be based on ADA recommendations, which call for maintaining HbA1c concentrations at <7%, or aiming for more stringent goals in persons who can reach those targets without experiencing significant hypoglycemia or other adverse treatment effects.

Higher HbA1c targets are recommended for children, adolescents and sometimes for patients with limited life expectancy, extensive comorbid illness, a history of severe hypoglycemia or advanced complications. Patients should undergo HbA1c testing at least twice a year, and quarterly if the treatment regimen has changed or if goals are not being met.

The value of HbA1c testing in diagnosing prediabetes was the focus of a longitudinal cohort study of men and women aged 24 to 82 years without diabetes at baseline. Using a controversial diagnostic criterion of 5.7% to 6.4%, screening by HbA1c alone missed 61% of the persons who were diagnosed with prediabetes when a combination of impaired fasting glucose levels and HbA1c was used.

“The predictive value for progression to diabetes assessed by HbA1c 5.7-6.4% was similar to that assessed by impaired fasting alone,” the researchers pointed out and suggested that using the two tests together could efficiently target people who are most likely to develop diabetes and allow for early intervention (Lancet. 2011;378:147-155).