Hemoglobin A1c, also called A1c or glycated hemoglobin, is hemoglobin with glucose attached. The A1c test evaluates the average amount of glucose in the blood over the last 2 to 3 months by measuring the percentage of glycated (glycosylated) hemoglobin.
Note: This article addresses diabetes mellitus, not diabetes insipidus . Although the two share the same reference term "diabetes" (which means increased urine production), diabetes insipidus is much rarer and has a different underlying cause.