What is HbA1c?

HbA1c (glycated hemoglobin) measures the percentage of hemoglobin in your blood that has glucose attached to it. Because red blood cells live for about 120 days, HbA1c provides a picture of your average blood sugar control over the past 2–3 months — making it the gold standard for diabetes monitoring.

Why is it Important?

Unlike a fasting glucose test that captures a single moment, HbA1c reveals long-term blood sugar trends. It is used to diagnose prediabetes and diabetes, and to monitor how well diabetes management plans are working. Every 1% reduction in HbA1c is associated with a significant decrease in diabetes-related complications.

Normal Ranges

Group	Range	Unit
Normal	< 5.7	%
Prediabetes	5.7 – 6.4	%
Diabetes	≥ 6.5	%
Normal	< 39	mmol/mol
Prediabetes	39 – 47	mmol/mol
Diabetes	≥ 48	mmol/mol

What Do Abnormal Results Mean?

High HbA1c

Common causes include:

Type 2 diabetes (most common)
Type 1 diabetes
Prediabetes (insulin resistance)
Poorly controlled diabetes
Iron deficiency (can falsely elevate results)
Splenectomy (red blood cells live longer)

Falsely Low HbA1c

Certain conditions can cause misleadingly low results:

Recent blood loss or transfusion
Hemolytic anemia (red blood cells destroyed faster)
Sickle cell disease or other hemoglobinopathies
Chronic kidney disease (erythropoietin therapy)
Pregnancy (increased red blood cell turnover)

When Should You Get Tested?

HbA1c should be tested every 3–6 months for people with diabetes, and annually for those with prediabetes or risk factors (obesity, family history, history of gestational diabetes). The American Diabetes Association recommends HbA1c screening for all adults starting at age 35, or earlier if risk factors are present.