The HbA1c test (also called A1c or glycated hemoglobin) is a blood test that estimates your average blood sugar (glucose) level over the past 2–3 months. It does this by measuring the percentage of hemoglobin (the oxygen-carrying protein inside red blood cells) that has glucose attached to it. Because red blood cells typically live about 120 days, the A1c reflects longer-term glucose control rather than what your blood sugar is at one moment.

In plain language: the A1c is like a “report card” for your recent blood sugar control. A higher HbA1c means your blood glucose has been higher on average, which can increase the risk of diabetes-related complications over time.

HbA1c results are reported as a percentage (%). While targets can vary by age, pregnancy status, and other medical conditions, common interpretation ranges include:

• Normal: below about 5.7%

• Prediabetes: about 5.7%–6.4%

• Diabetes: about 6.5% or higher (usually confirmed with repeat testing and/or additional glucose testing)

Many people with diabetes aim for an HbA1c goal (often around <7%), but the right goal is individualized with your clinician. The HbA1c does not require fasting, and it is often used alongside home glucose checks or continuous glucose monitoring (CGM) to understand both average levels and day-to-day patterns.

Important note: Certain conditions can make the HbA1c less accurate by affecting red blood cell lifespan or hemoglobin type (for example, iron deficiency anemia, recent blood loss or transfusion, hemoglobin variants such as sickle cell trait, kidney disease, or pregnancy). If this applies to you, your clinician may recommend alternative tests (such as fructosamine or CGM metrics).

Doctors commonly order an HbA1c (A1c) test to screen for diabetes, diagnose prediabetes/diabetes, and monitor long-term glucose control in people with known diabetes. Because it reflects average blood sugar over weeks to months, it helps guide treatment decisions such as lifestyle changes, oral diabetes medications, or insulin adjustments.

You may be tested if you have symptoms that can suggest high blood sugar, including:

• Increased thirst and frequent urination

• Unexplained weight loss

• Fatigue, blurry vision, or slow-healing cuts

• Frequent infections (such as yeast infections or skin infections)

It’s also commonly done if you have risk factors for type 2 diabetes or insulin resistance, such as:

• Overweight/obesity, especially increased waist circumference

• Family history of type 2 diabetes

• High blood pressure, high triglycerides, or low HDL (“good”) cholesterol

• History of gestational diabetes or delivering a large baby

• Polycystic ovary syndrome (PCOS)

• Physical inactivity

• Age-related risk (screening is commonly recommended starting in adulthood, earlier if risk is higher)

• Belonging to certain higher-risk ethnic groups (risk varies by population)

For people already diagnosed with diabetes, HbA1c is typically checked every 3 months when treatment is being changed or control is not at goal, and every 6 months when stable and at goal (your clinician may tailor this schedule). It helps estimate your risk for long-term complications, including eye, kidney, nerve, and cardiovascular problems.

• Type 2 diabetes mellitus

• Type 1 diabetes mellitus

• Prediabetes (impaired glucose regulation)

• Gestational diabetes (and postpartum diabetes risk assessment)

• Metabolic syndrome

• Insulin resistance

• Polycystic ovary syndrome (PCOS)

• Screening for diabetes and prediabetes as part of preventive care

• Tracking long-term blood sugar control (average glucose over 2–3 months)

• Evaluating how well lifestyle changes (nutrition, weight loss, exercise) are working

• Guiding diabetes medication adjustments and improving treatment adherence

• Reducing risk of diabetes complications (eye, kidney, nerve, and foot problems)

• Supporting cardiovascular risk reduction by improving overall metabolic health

• Monitoring health after gestational diabetes and planning future pregnancy care