HbA1c (glycosylated haemoglobin) and vitamin C

Some of the factors that influence HbA1c and its measurement

• 1. Erythropoiesis
  • Increased HbA1c: iron deficiency, vitamin B12 deficiency, decreased erythropoiesis
    
    
  • Decreased HbA1c: administration of erythropoietin, iron, vitamin B12, reticulocytosis, chronic liver disease
    
    
• 2. Altered Haemoglobin
  • Genetic or chemical alterations in haemoglobin: haemoglobinopathies, HbF, methaemoglobin, may increase or decrease HbA1c
    
    
• 3. Glycation
  • Increased HbA1c: alcoholism, chronic renal failure, decreased intraerythrocyte pH.
  • Decreased HbA1c: aspirin, vitamin C and E, certain haemoglobinopathies, increased intra-erythrocyte pH
  • Variable HbA1c: genetic determinants
    
    
• 4. Erythrocyte destruction
  • Increased HbA1c: increased erythrocyte life span: Splenectomy
    
    
  • Decreased HbA1c: decreased erythrocyte life span: haemoglobinopathies, splenomegaly, rheumatoid arthritis or drugs such as antiretrovirals, ribavirin and dapsone
    
    
• 5. Assays
  • Increased HbA1c: hyperbilirubinaemia, carbamylated haemoglobin, alcoholism, large doses of aspirin, chronic opiate use
    
    
  • Variable HbA1c: haemoglobinopathies
    
    
  • Decreased HbA1c: hypertriglyceridaemia

* Some of the above interfering factors are 'invisible' in certain of the available assays

Reference:

• WHO (2011).Use of Glycated Haemoglobin (HbA1c) in the Diagnosis of Diabetes Mellitus (Abbreviated Report of a WHO Consultation). WHO/NMH/CHP/CPM/11.1
• Diabetes UK. New diagnostic criteria for diabetes (Jan 2011) - Use of Haemoglobin A1c (HbA1c) in the diagnosis of diabetes mellitus in the UK