Glycosylated Hemoglobin Test (Hemoglobin A1c) Say: gly-koh-sih-lay-tid hee-muh-glow-bin test This blood test can tell someone with diabetes if his or her diabetes is under control or out of control. As a person's blood sugar gets higher, glucose attaches to hemoglobin (a substance inside red blood cells that carries oxygen to cells). When this happens, doctors say the hemoglobin has become glycosylated. The glucose remains attached to the hemoglobin for the life of the red blood cell, or about 2 to 3 months. This blood test measures the amount of glycosylated hemoglobin in the blood. In other words, it's a way of figuring out what the person's average blood glucose level was for the 2 to 3 months before the test. This can help determine how well a person's diabetes is being controlled over time. Back to Articles Related Articles Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor. © 1995-2021 KidsHealth®. All rights reserved. Images provided by The Nemours Foundation, iStock, Getty Images, Veer, Shutterstock, and Clipart.com.