HbA1c Explained: The 3-Month Blood Sugar Test
HbA1c reflects your average blood sugar over about 90 days — a single test that carries three months of information.
What HbA1c actually measures
Glucose binds irreversibly to hemoglobin inside red cells. Because red cells live about 120 days, the percentage of glycated hemoglobin (HbA1c) reflects the average glucose exposure over roughly the last 90 days.
Reference thresholds (Diabetes Canada): normal below 5.7% (39 mmol/mol), prediabetes 5.7–6.4% (39–46), diabetes 6.5% or above (48+). A single value above threshold is usually confirmed with a second measurement.
HbA1c vs fasting glucose
Fasting glucose is a snapshot; HbA1c is an average. They can disagree — someone with tight morning control but frequent post-meal spikes may have a normal fasting glucose and an elevated HbA1c. Using both together is more sensitive than either alone.
HbA1c is unreliable in conditions that shorten or lengthen red cell life: hemolytic anemia, recent transfusion, iron deficiency, chronic kidney disease with EPO, or certain hemoglobinopathies. In these cases, fructosamine or continuous glucose monitoring is preferred.
Prediabetes: the window for prevention
An HbA1c of 5.7–6.4% is not a diagnosis you accept and monitor — it is a window. Lifestyle interventions (structured nutrition, 150 minutes of moderate activity per week, 5–7% weight loss when applicable) reduce progression to type 2 diabetes by nearly 60% in landmark trials.
Add HbA1c to your next draw
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Frequently asked questions
Do I need to fast for HbA1c?+
No — HbA1c does not require fasting.
How often should HbA1c be repeated?+
Yearly for adults over 40 or with risk factors; every 3–6 months if diabetic and adjusting therapy.