Biomarker · Glucose

HbA1c (glycated haemoglobin)

Also known as: glycated haemoglobin, A1c, haemoglobin A1c, glycosylated haemoglobin

Haemoglobin that has glucose attached to it. Because red cells live about three months, the HbA1c fraction reports average blood glucose over the previous two to three months and is the marker used to diagnose and monitor type 2 diabetes.

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Also known as
glycated haemoglobin, A1c, haemoglobin A1c, glycosylated haemoglobin
Units
mmol/mol (IFCC) or % (DCCT); 48 mmol/mol = 6.5%
Measured by
HbA1c, Blood glucose, Full blood count

What it is and what it does

Glucose in the blood attaches to haemoglobin slowly and irreversibly, so the higher the average glucose, the larger the share of haemoglobin that is glycated. Because the red cell population turns over every 120 days or so, HbA1c averages glucose exposure across that period, with the most recent month weighing most. It is reported in mmol/mol (the IFCC standard used in the UK) or as a percentage (the older DCCT units used in the United States). Unlike a single glucose reading it does not need fasting and is not disturbed by what was eaten that morning.

Why it may be higher

  • Sustained high blood glucose: diabetes or prediabetes
  • Iron deficiency anaemia and other states with older red cells (falsely high)
  • Kidney failure, some haemoglobin variants (assay-dependent)

Why it may be lower

  • Recent blood loss, haemolysis or transfusion (younger red cells: falsely low)
  • Pregnancy, erythropoietin treatment, some haemoglobin variants
  • Improving glucose control

A high or low value can be associated with several different situations. The result is interpreted with other results, symptoms, history and clinical findings.

What can affect the result

  • Any condition that shortens or lengthens red-cell survival changes the value independently of glucose
  • Haemoglobin variants can interfere with some assay methods
  • It cannot show day-to-day swings or hypoglycaemia
Reference ranges. Reference intervals for this marker depend on the laboratory, the assay, the units, age, sex and pregnancy. Interpret a result against the interval printed on the laboratory report, not against a figure from the internet.

Medicines that can change it

AtorvastatinMetforminRosuvastatin

Each medicine page lists its effect on this marker under "Effects on tests and results", with the source.

Educational content. A biomarker page explains what a substance is and why its level can change. It cannot determine the cause of your result: interpret a result using the range supplied by the laboratory that performed the test, with the clinician who ordered it.