A1C (Hemoglobin A1C)

A blood test that measures average blood glucose levels over the past 2–3 months — used to diagnose and monitor diabetes.

Hemoglobin A1C (HbA1c, glycated hemoglobin) is a blood test that reflects average blood glucose levels over the past 2–3 months by measuring the percentage of hemoglobin that has glucose chemically attached. The American Diabetes Association classifies A1C results as: normal (<5.7%), prediabetes (5.7–6.4%), and diabetes (≥6.5%). A1C is the standard test for diagnosing type 2 diabetes and monitoring glycemic control in people with diabetes. Most diabetes treatment guidelines target an A1C of <7.0% for most adults with diabetes, though targets are individualized. GLP-1 receptor agonists like semaglutide and tirzepatide consistently lower A1C by 1.0–2.0 percentage points in clinical trials, in addition to their weight-loss effects. People with prediabetes who lose 5–10% of their body weight through lifestyle changes (or GLP-1-assisted weight loss) can significantly reduce their risk of progressing to type 2 diabetes.

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This glossary is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your individual health.