A1C

A1C (also HbA1c, glycated hemoglobin): A1C (also written HbA1c) is a blood test that measures the percentage of hemoglobin in your red blood cells that has been bound to glucose. Because red blood cells live for roughly three months, A1C reflects your average blood sugar over that period — not just one moment.

How it's reported

A1C is reported as a percentage. The American Diabetes Association uses these cutoffs: under 5.7% is normal, 5.7–6.4% is prediabetes, and 6.5% or higher (confirmed) is diabetes. Many labs also report an "estimated average glucose" (eAG) in mg/dL alongside the percentage.

Treatment targets

For most non-pregnant adults with diabetes, the ADA suggests an A1C target under 7%. Tighter targets (under 6.5%) are reasonable for some patients without significant hypoglycemia. Looser targets are appropriate for older adults, those with limited life expectancy, or extensive comorbidities.

Why it matters for carb counting

A1C is the long-term scorecard for your day-to-day decisions, including how accurately you count carbs. A1C improvements typically follow 6–12 weeks of consistent meal-time accuracy.