A1C, also called HbA1c, is a blood test that estimates average blood sugar over about the past 2 to 3 months. It can help diagnose prediabetes or diabetes and can also help monitor diabetes over time.
Quick summary
A1C is useful because it does not require fasting, but it is not perfect. Pregnancy, some types of anemia, hemoglobin variants, kidney disease, recent blood loss, transfusion, and other factors can make results harder to interpret.
Key takeaways
- A1C can be used to diagnose diabetes and prediabetes in many adults.
- A result in the diabetes range usually needs confirmation if symptoms are absent.
- Fasting glucose or an oral glucose tolerance test may be needed when A1C is unreliable.
- A1C also helps monitor diabetes, but it does not show daily highs and lows.
What the numbers mean
Common diagnostic cutoffs are below 5.7 percent for normal, 5.7 to 6.4 percent for prediabetes, and 6.5 percent or higher for diabetes. A clinician may repeat the test or use another test to confirm the diagnosis.
For people already living with diabetes, the A1C goal is individualized. Many adults use a goal near 7 percent, but the right target may be higher or lower depending on age, pregnancy, low-blood-sugar risk, other medical conditions, and treatment burden.
When A1C may not be enough
- Symptoms suggest diabetes but A1C is not in the diabetes range.
- A1C and finger-stick or CGM patterns do not match.
- Pregnancy or recent blood loss is present.
- A hemoglobin condition or anemia may affect the result.
- You need to understand meal-related spikes or low blood sugar.
Practical takeaway
A1C is a helpful test, not the whole story. Ask whether the result needs confirmation and whether another glucose test would answer a different question.
Safety note
This article is not a substitute for medical care. Seek urgent care for vomiting, dehydration, confusion, deep or rapid breathing, severe weakness, or symptoms that feel dangerous.
What to ask your care team
- Does my A1C need confirmation?
- Could any health condition make my A1C less reliable?
- Should we compare A1C with fasting glucose, OGTT, finger-stick readings, or CGM data?
Related reading
Source summary
- Diabetes Tests and Diagnosis, National Institute of Diabetes and Digestive and Kidney Diseases. Patient guidance. Accessed June 5, 2026. Source
- The A1C Test and Diabetes, National Institute of Diabetes and Digestive and Kidney Diseases. Patient guidance. Accessed June 5, 2026. Source
- Diabetes Testing, Centers for Disease Control and Prevention. Patient guidance. Accessed June 5, 2026. Source
- A1C Test for Diabetes and Prediabetes, Centers for Disease Control and Prevention. Patient guidance. Accessed June 5, 2026. Source