Understanding Hemoglobin A1c

This article explains what the A1c test measures, how it differs from a fingerstick glucose reading, and how clinicians use it.

What A1c Measures

Hemoglobin A1c measures the percentage of hemoglobin — a protein in red blood cells — that has glucose attached to it. Because red blood cells live about three months, the A1c reflects average blood sugar over roughly the previous three months, rather than the level at one moment.

A1c Versus a Glucose Reading

A fingerstick or laboratory glucose shows blood sugar right now; it swings with meals, activity, illness, and stress. The A1c smooths those swings into a longer-term average. The two tests answer different questions, and care often uses both.

How the Ranges Are Commonly Described

Below 5.7% — within the range considered normal
5.7% to 6.4% — described as prediabetes, a signal that risk is elevated and prevention matters
6.5% or higher — within the range used to diagnose diabetes, typically confirmed with repeat or additional testing

These are general categories; interpretation always belongs with your own clinician, and certain conditions affecting red blood cells can make the A1c less reliable.

How A1c Guides Treatment

For people with diabetes, the A1c is the central long-term control measure. Targets are individualized: a common goal is below 7%, while a less strict goal may be appropriate for older adults or those with other serious conditions. The test is usually repeated every three to six months depending on stability.

Questions Patients Often Ask

Why did my A1c stay high when my morning sugars look good?

Morning readings capture one moment. Blood sugar may be rising after meals or overnight without appearing in a morning check. Your clinician may suggest checking at additional times or reviewing continuous-glucose data if available.

Can I lower my A1c quickly before a test?

Not meaningfully — the test reflects months of average blood sugar, which is also why it is useful. Sustainable changes in nutrition, activity, and medication adherence are what move it.

Is prediabetes guaranteed to become diabetes?

No. Structured lifestyle change — particularly modest weight loss and regular activity — substantially reduces progression for many people. Prediabetes is best treated as an actionable warning, not a sentence.

Medical information notice: this page provides general educational information and is not a substitute for individualized medical advice, diagnosis, or treatment. Recommendations vary by age, history, medications, and examination findings.

Medically reviewed by Kanwar Partap Singh Gill, MD, family medicine physician in Fresno, California · Published July 18, 2026 · Last reviewed July 20, 2026