Is HbA1c useful for blood sugar?

HbA1c is a well-validated clinical marker reflecting average blood glucose over the preceding 2–3 months. It is widely used for diagnosing and monitoring diabetes mellitus. Evidence is strong (numerous clinical trials, guidelines). However, limitations exist: HbA1c can be affected by anemia, kidney disease, hemoglobin variants, or certain medications. In consumer self-tests (e.g., fingerstick), accuracy may be lower compared to venous blood draws in a laboratory. For a reliable assessment of glucose metabolism, HbA1c is useful but not sufficient alone – complementary tests (fasting glucose, oral glucose tolerance test) may be needed.