Hemoglobin A1c reflects how much glucose has coated your red blood cells over the past few months. Because it captures round‑the‑clock exposure, it mirrors how glucose is affecting vessels, nerves, kidneys, eyes, and the heart—not just on the day of a blood draw.In most adults, values below about 5.7 align with normal glucose regulation, 5.7–6.4 suggests prediabetes, and 6.5 or higher indicates diabetes. For long‑term risk, “optimal” generally sits toward the low end of the normal range without drifting into hypoglycemia. When A1c is unusually low, it may mean genuinely low average glucose—sometimes with shakiness, sweating, or confusion from hypoglycemia—or it may reflect shorter red‑cell lifespan (hemolysis, blood loss, some kidney or liver disease), which makes A1c look lower than true glucose exposure. Iron deficiency often raises A1c spuriously; treatment and hemoglobin variants can shift readings in either direction.When A1c is elevated, it signals chronic hyperglycemia. Excess glucose glycation stiffens proteins, injures capillaries, and accelerates atherosclerosis, increasing risk for retinopathy, nephropathy, neuropathy, heart attack, and stroke. People may notice thirst, frequent urination, fatigue, blurry vision, slow healing, or infections. In pregnancy, higher A1c early relates to congenital risks and later to high fetal growth and maternal complications. In children and teens, puberty‑related insulin resistance can push A1c upward even before symptoms.Big picture: A1c integrates metabolism, red‑cell biology, and vascular health. It complements fasting glucose, oral glucose tests, and continuous monitoring, and is best interpreted alongside anemia status, kidney function, and hemoglobin traits. Over time, lower A1c within the healthy range tracks with fewer microvascular and cardiovascular events.
