HbA1c vs. fasting glucose

Both tests measure blood sugar, but they answer different questions. Understanding the difference helps you read your results — and catch trouble early.

Fasting glucose — a snapshot

This is your blood sugar at a single moment after an overnight fast. It's quick and cheap, but it can be nudged by stress, sleep, and what you ate yesterday. Normal is under 100 mg/dL; 100–125 is prediabetes range; 126+ on two occasions suggests diabetes.

HbA1c — the rolling average

Hemoglobin A1c reflects your average blood sugar over the previous 2–3 months, because glucose sticks to red blood cells over their lifespan. It doesn't require fasting and is less swayed by day-to-day noise. Under 5.7% is normal; 5.7–6.4% is prediabetes; 6.5%+ indicates diabetes.

Why use both

They can disagree — and that disagreement is informative. Together they give a fuller picture of your metabolic health, and adding fasting insulin can reveal insulin resistance years before glucose climbs.

This article is for general education and is not medical advice. Consult a qualified healthcare provider about your results. Read about how we write about lab testing.