The glycated hemoglobin (A1C) blood test measures how thick the coat of glucose is that is bound to the blood's hemoglobin (or blood sugar levels). When the two bind, the hemoglobin gets a coat of sugar around it. The coat thickens as the amount of glucose in the blood increases. The hemoglobin A1C test measures for HbA1C, a subtype of hemoglobin.
Hemoglobin is a protein found inside the red blood cells (RBCs), and its main job is to transport oxygen. It also is responsible for giving blood its red color. There are multiple types of hemoglobin, but its main form is hemoglobin A. Glucose spontaneously binds to hemoglobin as it circulates the blood, this is called glycated hemoglobin, and its predominant form is referred to as A1C. When glucose binds to the hemoglobin, it’s there for the entire life of the red blood cell (usually about four months). The more glucose that’s in the blood, the more glycated hemoglobin is created. A1C is produced on a daily basis and additionally, it dies on a daily basis as older RBCs die and are replaced with younger RBCs that have not yet been affected by glucose.