HbA1c reflects glycation of red cells over their lifespan, so anything that changes red cell survival or haemoglobin structure distorts it.
Iron deficiency tends to raise HbA1c, while haemolysis, recent blood loss or transfusion, and erythropoietin treatment lower it. Haemoglobin variants can interfere depending on the laboratory method. Late pregnancy and advanced chronic kidney disease also make it unreliable.
Iron deficiency anaemia and haemoglobinopathies are common in India, so this comes up often. Where HbA1c and glucose readings disagree, believe the glucose and confirm with plasma glucose or an OGTT.
- Check a full blood count before relying on a borderline HbA1c
- Iron deficiency can push HbA1c up; haemolysis, bleeding and transfusion push it down
- Use plasma glucose or an OGTT for diagnosis in pregnancy, advanced CKD or known haemoglobinopathy
- If HbA1c and home or lab glucose disagree, investigate rather than average them
Why it matters
A falsely high or low HbA1c can create or hide a diabetes diagnosis.
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