HbA1c methods and Hemoglobin Variants (HbS, HbC and HbE traits)

HbA1c, also call A1C, is a measure of the amount of glucose attached to hemoglobin (Hb) in red blood cells.  The higher the glucose levels over the previous 2-3 months, the higher the A1C.  The A1C test is used to monitor the glucose levels of patients who have been diagnosed with diabetes.  In people who have hemoglobin variants such as HbS (sickle cell trait), some A1C tests give falsely high or low readings that can lead to the over-treatment or under-treatment of diabetes. 

Laboratories use over 20 different methods for measuring A1C, but some of these methods can give inaccurate results when the patient has a hemoglobin variant such as sickle cell trait.  Doctors or patients interested in getting information about the accuracy of a particular A1C method for patients with hemoglobin variants should first find out which method your laboratory is using. 

The following table lists the 19 methods most often used to measure A1C and whether the method is affected by either HbS or HbC or HbE trait.  Methods are listed in alphabetical order by manufacturer.  If your diabetes patient has a hemoglobin variant, your lab should use one of the methods that does not show interference from the variant, thus producing an accurate A1C result.

*This method is being replaced by the Roche Cobas Integra Gen 2

More comprehensive information regarding HbA1c assay interferences

More (from the NIDDK web site):
Sickle Cell Trait and Other Hemoglobinopathies and Diabetes: Important Information for Physicians
For People of African, Mediterranean, or Southeast Asian Heritage: Important Information about Diabetes Blood Tests