A1C vs Fasting Glucose vs OGTT: Which Test Means What?
If you’ve ever looked at your labs and thought, “Why does my A1C say prediabetes while my fasting glucose looks fine?”—I’ve been there.
Why these tests don’t always match
They measure different things: an average (A1C), a baseline snapshot (fasting), and a glucose “stress test” (OGTT).
A1C
A1C reflects ~2–3 months.
Fasting glucose
Fasting can be influenced by sleep, stress, illness, alcohol, and the dawn phenomenon.
OGTT
Some people handle fasting fine but struggle after meals—OGTT can catch that earlier.
Related: Prediabetes Basics