What is a normal A1c?

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The A1c - glycated hemoglobin - measures how much sugar is stuck to your red blood cells, and since red cells live about three months, it reads as your average blood sugar over that window. NIDDK's cutoffs: below 5.7 percent is normal; 5.7 to 6.4 is prediabetes; 6.5 and above, confirmed on a repeat test, is diabetes. Each point maps to an average glucose: 5.7 percent is roughly 117 mg/dL, 6.5 percent roughly 140, 8 percent roughly 183.

What moves it: sustained glucose patterns, not yesterday's dessert - which is why it beats a single fasting reading for diagnosis. An A1c in the prediabetes range is a genuine fork in the road: lifestyle change at that stage meaningfully lowers progression, per NIDDK prevention evidence.

When the A1c misleads: anything that changes red blood cell lifespan skews it - anemia and recent blood loss can lower it falsely, iron deficiency and older age can nudge it up, and common hemoglobin variants in some ancestries distort it. In those cases, providers use fasting glucose, an oral glucose tolerance test, or fructosamine instead. Pregnancy uses different tests entirely. One more framing: the A1c is an average, so it can hide wild daily swings - someone oscillating between highs and lows can show a deceptively normal number, which is where glucose monitoring adds the picture the average misses.

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