Glycated Hemoglobin (HbA1c): What It Shows, Values, and Interpretation

Hemoglobin is the protein in red blood cells that carries oxygen. Some of the glucose in the blood binds to hemoglobin, and the HbA1c test measures the percentage of hemoglobin with glucose attached. The higher blood glucose levels have been, the higher the HbA1c value tends to be.

Because red blood cells circulate in the body for approximately 120 days, the result provides information over a longer period than a standard blood glucose test. However, recent weeks have a greater influence on the result than earlier months. HbA1c does not separately show brief episodes of very high or very low blood glucose.

For adults who are not pregnant, the ranges used for diagnosis are: below 5.7% for values considered normal, between 5.7% and 6.4% for prediabetes, and at least 6.5% for diabetes. These thresholds must be considered alongside the clinical situation and how the test was performed.

In the absence of obvious symptoms or unequivocal hyperglycemia, a diagnosis is not made on the basis of a single abnormal value. The doctor may recommend repeating the HbA1c test or confirming the result with a fasting blood glucose test or an oral glucose tolerance test.

A medical consultation is recommended when HbA1c is at least 5.7%, when the value has increased compared with previous test results, or when the result does not match blood glucose readings taken at home. The doctor will interpret the test together with risk factors, symptoms, family history, and other available investigations.

An evaluation is also important if symptoms such as increased thirst, frequent urination, unintentional weight loss, persistent fatigue, or blurred vision are present. These symptoms do not confirm diabetes on their own, but they warrant medical investigation.

Tell your doctor if you have anemia, kidney or liver disease, a hemoglobin variant, recent bleeding, a blood transfusion, or treatment with erythropoietin. In these situations, HbA1c may be less accurate, and diagnosis may require the use of plasma glucose values.

During pregnancy, HbA1c has specific limitations and does not replace the tests recommended for detecting gestational diabetes. The result should be discussed with the doctor overseeing the pregnancy.

When only HbA1c is being tested, fasting is generally not required. If the doctor has also recommended a fasting blood glucose test, lipid profile, or other tests on the same day, follow the instructions provided for the entire set of investigations.

It is useful to bring previous test results, a list of current treatments, and, if available, blood glucose readings taken at home or continuous glucose monitoring records to the consultation. Changes over time may be more relevant than a single value considered in isolation.

For prediabetes, the monitoring schedule is determined according to the initial value and individual risk factors. For people with diabetes, HbA1c is frequently checked at least twice a year and more often when treatment changes or individual targets are not met.

The HbA1c target is not the same for everyone. It is established together with the doctor based on age, duration of diabetes, risk of hypoglycemia, associated conditions, and current treatment. Do not change your medication solely on the basis of the result without medical advice.