nded as the cut-off point for diagnosing diabetes. A value less than 48 mmol/mol (6.5%) does not exclude diabetes diagnosed using glucose tests. One advantage of using HbA1c for diagnosis is that the test does not require a fasting blood sample.
Situations where HbA1c is not appropriate for diagnosis of diabetes include:
Children and young people.
Patients suspected of having type 1 diabetes.
Patients with symptoms of diabetes for less than two months.
Patients at high diabetes risk who are acutely ill.
Patients taking medication that may cause rapid glucose rise – eg, steroids, antipsychotics.
Patients with acute pancreatic damage, including pancreatic surgery.
Presence of other factors that influence HbA1c and its measurement:
Increased HbA1c: iron deficiency, vitamin B12 deficiency, decreased erythropoiesis.
Decreased HbA1c: administration of erythropoietin, iron, vitamin B12, reticulocytosis, chronic liver disease.
Genetic or chemical alterations in haemoglobin: haemoglobinopathies, HbF and methaemoglobin may increase or decrease HbA1c.
Increased HbA1c: alcoholism, chronic kidney disease.
Decreased HbA1c: aspirin, vitamin C and vitamin E, certain haemoglobinopathies.
Increased HbA1c: increased erythrocyte lifespan – eg, splenectomy.
Decreased HbA1c: decreased erythrocyte lifespan – eg, haemoglobinopathies, splenomegaly, rheumatoid arthritis or drugs such as antiretrovirals, ribavirin and dapsone.
Increased HbA1c: hyperbilirubinaemia, alcoholism, large doses of aspirin, chronic opiate use.
Variable HbA1c: haemoglobinopathies.
Decreased HbA1c: hypertriglyceridaemia