Expansion
Reflects average glucose over the preceding 8 to 12 weeks
Expansion
HbA1c is non-enzymatic glycation of haemoglobin, proportional to average glucose over the life of the red cell, so it reflects the previous 8 to 12 weeks, weighted towards the most recent month.
Falsely LOW (shortened red cell survival or increased turnover)
- Haemolysis, recent blood loss or transfusion
- Splenomegaly
- Pregnancy
- Erythropoietin, iron or B12 therapy (new cells dilute the glycated pool)
- Chronic kidney disease and liver disease
Falsely HIGH
- Iron deficiency, B12 or folate deficiency (older cells persist)
- Splenectomy
- Alcohol, chronic salicylate use
Unreliable entirely: haemoglobinopathies (assay dependent), and any acute change in glycaemia within the last 6 weeks, which is why it cannot be used to diagnose or monitor acute presentations such as new type 1 diabetes or steroid-induced hyperglycaemia.
Where HbA1c is unreliable, fructosamine (reflecting 2 to 3 weeks) or continuous glucose monitoring is used instead.