HbA1c
HbA1c, also called glycated hemoglobin, is a lab test that measures what percentage of hemoglobin in your red blood cells has glucose (sugar) bonded to it. MedlinePlus+2Healthdirect+2
Because red blood cells live for about 2–3 months, the HbA1c level reflects the average blood sugar over that timeframe. KidsHealth+1
The test is widely used both for diagnosing diabetes and for monitoring long-term glucose control.