Glycosylated hemoglobin, also known as HbA1c, is a form of hemoglobin that is chemically linked to sugar molecules. It forms when glucose in the blood attaches to hemoglobin, the protein in red blood cells that carries oxygen. The level of HbA1c in the blood reflects average blood sugar levels over the past two to three months, making it a useful marker for managing diabetes. Healthcare providers often use HbA1c tests to monitor how well a person's blood sugar levels are controlled. A higher percentage of glycosylated hemoglobin indicates poorer blood sugar control, which can lead to complications associated with diabetes, such as heart disease and nerve damage.