Glycosylated Hemoglobin Test (Hemoglobin A1c) Hemoglobin is the substance inside red blood cells that carries oxygen to the cells of the body. Glucose (a type of sugar) molecules in the blood normally become stuck to hemoglobin molecules - this means the hemoglobin has become glycosylated (also referred to as hemoglobin A1c, or HbA1c). As a person's blood sugar becomes higher, more of the person's hemoglobin becomes glycosylated. The glucose remains attached to the hemoglobin for the life of the red blood cell, or about 2 to 3 months. A blood test can measure the amount of glycosylated hemoglobin in the blood. The glycosylated hemoglobin test shows what a 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.