Methods and criteria for diagnosing diabetes
- Diabetes symptoms (e.g. polyuria, polydipsia and unexplained weight loss for Type 1) plus:
- a random venous plasma glucose concentration ≥ 11.1 mmol/l or
- a fasting plasma glucose concentration ≥ 7.0 mmol/l (whole blood ≥ 6.1 mmol/l) or
- two hour plasma glucose concentration ≥ 11.1 mmol/l two hours after 75g anhydrous glucose in an oral glucose tolerance test (OGTT).
- With no symptoms diagnosis should not be based on a single glucose determination but requires confirmatory plasma venous determination. At least one additional glucose test result on another day with a value in the diabetic range is essential, either fasting, from a random sample or from the two hour post glucose load. If the fasting random values are not diagnostic the two hour value should be used.
The criteria for diagnosing gestational diabetes is different. Gestational diabetes should be diagnosed if the woman has either:
- a fasting plasma glucose level of 5.6mmol/l or above or
- a 2-hour plasma glucose level of 7.8mmol/l or above.
Haemoglobin A1c (HbA1c) testing to diagnose diabetes
An HbA1c of 48mmol/mol (6.5%) is recommended as the cut off point for diagnosing diabetes. A value of less than 48mmol/mol (6.5%) does not exclude diabetes diagnosed using glucose tests.
Finger-prick HbA1c should not be used unless the methodology and the healthcare staff and facility using it can demonstrate within the national quality assurance scheme that they match the quality assurance results found in laboratories. Finger prick tests must be confirmed by laboratory venous HbA1c in all patients.
In patients without symptoms of diabetes the laboratory venous HbA1c should be repeated. If the second sample is <48mmol/mol (6.5%) the person should be treated as at high risk of diabetes and the test should be repeated in 6 months or sooner if symptoms develop.
Situations where HbA1c is not appropriate for diagnosis of diabetes:
- ALL children and young people
- patients of any age suspected of having Type 1 diabetes
- patients with symptoms of diabetes for less than 2 months
- patients at high risk who are acutely ill (e.g. those requiring hospital admission)
- patients taking medication that may cause rapid glucose rise e.g. steroids, antipsychotics
- patients with acute pancreatic damage, including pancreatic surgery
- in pregnancy
- presence of genetic, haematologic and illness-related factors that influence HbA1c and its measurement (see annex 1 of the WHO report for a list of factors which influence HbA1c and its measurement)
Patients whose HbA1c is under 48 mmol/mol (6.5%)
- These patients may still fulfill WHO glucose criteria for the diagnosis of diabetes
- Use WHO glucose testing in patients who have symptoms of diabetes or clinically are at very high risk of diabetes. The use of such glucose tests is not recommended routinely in this situation.