Hemoglobin A1c: Making It Easier To Diagnose Diabetes

Screening and diagnosis of diabetes mellitus has long been based on the results of glucose tolerance testing and fasting blood glucose measurement. In 2009, however, experts recommended the use of hemoglobin A1c for the diagnosis of type 2 diabetes mellitus in nonpregnant adults. The diagnosis of diabetes mellitus can now be established if the hemoglobin A1c value is 6.5% or higher, provided that a confirmatory test reveals similar findings.

For clinicians, this is a welcome development. Performing glucose tolerance testing has never been practical, and the fasting blood glucose measurement required the patient to, of course, fast. Given the fact that hemoglobin A1c testing has been available for years, clinicians often wondered why the test was not endorsed for screening and diagnosis of diabetes mellitus. Lack of assay standardization prevented adoption of the test for this purpose in 1997 and 2003 when previous guidelines were published. In recent years, research comparing the accuracy and precision of the hemoglobin A1c test to glucose testing has shown equivalence, paving the way for the new recommendation.

Clinicians should be aware of some important limitations of the test. Spurious or misleading values may be obtained in patients with certain forms of anemia, hemoglobinopathies, and recent red blood cell transfusion. Fasting blood glucose measurement and oral glucose tolerance testing remain available for diagnosis when the hemoglobin A1C can not be measured.

References

Nathan D, et al. International Expert Committee report on the role of the A1c assay in the diagnosis of diabetes. Diabetes Care 2009; 32; 1327-34.


Visit: Clinician’s Guide to Laboratory Medicine: Pocket website