Hemoglobin A1c is the measurement of glycated hemoglobin and can aid in both the 
diagnosis and continued management of diabetes mellitus. Accurate glycosylated 
hemoglobin A1c (A1c) measurements are an essential part of decision making in 
the diagnosis and treatment of type 2 diabetes mellitus. Although national 
standards exist to eliminate technical error with A1c testing, multiple patient 
conditions can falsely decrease or elevate the A1c. In this review, we discuss 
the methods to measure A1c and the corresponding conditions that can affect the 
clinical utility of the test. Conditions that affect the A1c can be either those 
that impair erythrocyte production or alter the normal process of glycation. 
Some variation also has been associated with patient ethnicity and even with 
normal aging. We describe alternatives to A1c testing for the above clinical 
scenarios in an effort to make the practicing clinician aware of alternatives 
for glucose evaluation.