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Hemoglobin A1c, commonly known as HbA1c or glycated hemoglobin, is a laboratory test that measures the average blood sugar levels over the past two to three months. This test works by detecting glucose molecules that have attached to hemoglobin, the oxygen-carrying protein in red blood cells. Since red blood cells live for approximately 120 days, the HbA1c test provides a long-term picture of blood glucose control, making it more useful than daily blood sugar measurements that only show glucose levels at a single point in time.

The HbA1c test is primarily used to diagnose diabetes and prediabetes, as well as to monitor how well diabetes is being managed. For people without diabetes, normal HbA1c levels are typically below 5.7 percent. A result between 5.7 and 6.4 percent indicates prediabetes, which means blood sugar levels are higher than normal but not yet high enough to be classified as diabetes. An HbA1c level of 6.5 percent or higher on two separate tests indicates diabetes. For individuals already diagnosed with diabetes, the American Diabetes Association generally recommends maintaining an HbA1c level below 7 percent, though target levels may vary based on individual circumstances.

The test requires a simple blood sample and does not require fasting, making it convenient for patients. Healthcare providers typically recommend that people with diabetes have their HbA1c tested at least twice a year if their blood sugar levels are stable and meeting treatment goals. More frequent testing, such as every three months, may be necessary for those whose treatment plan has changed or who are not meeting their blood sugar targets. The test results help doctors adjust medications, diet, and exercise recommendations to improve diabetes management.

Several factors can affect HbA1c test results and should be considered when interpreting the values. Conditions that affect red blood cell turnover, such as recent blood loss, blood transfusions, certain types of anemia, or kidney disease, can lead to inaccurate results. Additionally, certain genetic variants of hemoglobin may interfere with some testing methods. People with these conditions may need alternative tests to monitor their blood sugar control. Despite these limitations, the HbA1c test remains one of the most valuable tools for assessing long-term glucose control and reducing the risk of diabetes-related complications.