HbA1c to diagnose diabetes

  • 48 mmol/mol is the cut-off for diagnosis of diabetes but, as with fasting glucose, should be rechecked unless clear clinical symptoms exist.
  • 42 – 47 equates to ‘high risk of diabetes’ – intensive lifestyle management, recheck annually.
  • <42 – may still be at high risk depending on clinical picture – consider need for lifestyle advice/retesting (3-yearly in this case).

Check with glucose test only if HbA1c <48 but either 1. clear clinical picture DM or 2. very high risk. Glucose tests not normally recommended when HbA1c is 48 or higher, but, to confuse matters, in one study in elderly patients (Rancho Bernado) 85% of the people found to have HbA1c at this level were then found not to be diabetic on glucose testing.

Situations in which HbA1c is inappropriate to use mainly stem from the fact that it may miss recent-onset significant changes in blood glucose.

  • Young people, or other suspicion of Type 1 diabetes
  • Short duration of symptoms (<2 months)
  • Pregnant, or <2 months post-partum
  • Short-term use (<2 months) of steroids/antipsychotics that affect glucose level. (Can be used in patients who have been stable on these for >2 months)
  • Pancreatic surgery or acute pancreatic trauma
  • Acute illness
  • Renal failure
  • HIV

Cautions appropriate in:

  • Untreated iron-deficiency anaemia (causes overestimate)
  • Haemolytic anaemia (causes underestimate)
  • Haemoglobinopathies (the test may detect and compensate for these but it depends entirely on which test and which haemoglobinopathy, so don’t count on this happening)
  • Recent commencement of erythropoetin treatment (causes underestimate)
  • Splenectomy (causes underestimate as increases red cell lifespan)

Note that age and race can affect results – Afro-Caribbeans/South Asians normally have HbA1c 4 mmol higher on average than Caucasians with equivalent blood glucose levels.

From Diabet Med 2012;29(11):1350 – 7) Use of HbA(1c) in the diagnosis of diabetes mellitus in the UK. The implementation of World Health Organisation guidance 2011

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About Dr Sarah

I'm a GP with a husband and two young children.
This entry was posted in Credits 2012, Diabetes, Endocrinology. Bookmark the permalink.

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