An HbA1c test uses a blood sample to show how blood sugar has been running over roughly the past two to three months. A doctor may request it when checking for diabetes or following up on treatment. Fasting is generally unnecessary for HbA1c itself, so check whether a separate fasting test is on your prescription before deciding when to visit the laboratory.

An HbA1c result is usually reported as a percentage and answers a different question from a glucose reading taken on the same day. It reflects a longer period, while the glucose reading describes that moment. Tell your clinician if you have a blood condition or recently had a blood transfusion, since these can affect interpretation. Your doctor can explain how to read the HbA1c alongside any other glucose results you have. If this is a follow-up, take the previous report so your clinician can compare the two results.