Hemoglobin A1c is a blood test that measures the average level of glucose in a person's blood over the past two to three months. It specifically looks at the percentage of hemoglobin, a protein in red blood cells, that is coated with sugar. This test is commonly used to diagnose and monitor diabetes. A higher A1c level indicates poorer blood sugar control, which can lead to complications if not managed properly. Healthcare providers often recommend regular testing for individuals with diabetes to help guide treatment decisions and assess the effectiveness of lifestyle changes or medications.