Biomarker education
A1C: What It Measures & Why People Track It
Also called: Hemoglobin A1c, HbA1c, Glycated hemoglobin
A1C is a blood test that reflects average blood glucose over roughly the prior two to three months.
General biomarker education — not personalized medical advice. Learn more
Result on your report
IllustrativeA1C
5.4%
Range: 4.0 – 5.6
Tracking over time
Illustrative| Date | Value |
|---|---|
| 2022 | 6.1 |
| 2023 | 5.8 |
| 2024 | 5.5 |
| 2025 | 5.3 |
What it generally measures
Glucose in the bloodstream can attach to hemoglobin in red blood cells. A1C (also called hemoglobin A1c, HbA1c, or glycated hemoglobin) estimates the percentage of hemoglobin that is glycated. Because red cells live for months, clinicians often use it as a longer-window view than a single fasting glucose.
Common units on reports: %
Why people track it over time
People often track A1C across visits because it summarizes a longer period than a one-day glucose reading. Trends can help you notice change before an appointment — they do not, by themselves, diagnose a condition.
Changes over time do not by themselves establish a diagnosis. Learn more
Questions you might ask a healthcare professional
Questions to bring
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What this page does not do
Conditions that change red-cell lifespan — including some anemias, recent transfusion, kidney disease, or hemoglobin variants — can make A1C harder to interpret. Public health agencies publish category cutoffs used in clinical practice; your report and clinician remain the source of interpretation for you. This page does not diagnose diabetes or prediabetes.
Further reading
Common questions
- What is A1C on a blood test?
- A1C is a blood test that reflects average blood glucose over roughly the prior two to three months. It is reported as a percent on most U.S. laboratory reports.
- Is A1C the same as glucose?
- No. Glucose is a snapshot at the time of the draw. A1C summarizes a longer window. Metabolic monitoring often includes both because they answer different timing questions.
- Do I need to fast for an A1C test?
- A1C usually does not require fasting. If it was drawn with other tests that do, follow those instructions.
- Why might A1C not match my glucose readings?
- They measure different time windows. Red-cell conditions can also affect A1C. Ask your clinician how to read them together for you.