Use of Haemoglobin A1c (HbA1c) in the diagnosis of diabetes mellitus in the UK
Diabetes UK welcomes decision by the World Health Organisation (WHO) to accept the use of the HbA1c test in diagnosing diabetes.
This report is an addendum to the diagnostic criteria published in the 2006 WHO/IDF report "Definition and diagnosis of diabetes mellitus and intermediate hyperglycaemia", and addresses the use of HbA1c in diagnosing diabetes mellitus. This report does not invalidate the 2006 recommendations on the use of plasma glucose measurements to diagnose diabetes.
Both reports can be found under 'Related information'.
WHO Recommendation 2011
HbA1c can be used as a diagnostic test for diabetes providing that stringent quality assurance tests are in place and assays are standardised to criteria aligned to the international reference values, and there are no conditions present which preclude its accurate measurement.
An HbA1c of 48 mmol/mol (6.5%) is recommended as the cut point for diagnosing diabetes. A value of less than 48 mmol/mol (6.5%) does not exclude diabetes diagnosed using glucose tests.
The following is practical guidance in order to help implement WHO guidance in the UK. Final guidance will be produced by the Association for Clinical Biochemistry:
- 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 repeat the laboratory venous HbA1c. If the second sample is <48 mmol/mol (6.5%) treat as high diabetes risk and repeat the test 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 diabetes 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 from WHO report
Patients whose HbA1c is under 48 mmol/mol (6.5%)
- These patients may still fulfil WHO glucose criteria for the diagnosis of diabetes.
- Use WHO glucose testing in patients with symptoms of diabetes or clinically at very high risk of diabetes.
- The use of such glucose tests is not recommended routinely in this situation.
The following is recommended for those at high risk of developing diabetes:
- High diabetes risk HbA1c 42-47 mmol/mol (6.0 – 6.4%)
- Provide intensive lifestyle advice
- Warn patients to report symptoms of diabetes
- Monitor HbA1c annually
- HbA1c under 42 mmol/mol (6.0%)
- These patients may still have high diabetes risk.
- Review the patient’s personal risk and treat as “high diabetes risk” as clinically indicated.
See below for previous WHO criteria:
Methods and criteria for diagnosing diabetes mellitus
1. Diabetes symptoms (ie polyuria, polydipsia and unexplained weight loss) plus
- a random venous plasma glucose concentration > 11.1 mmol/l
or
- a fasting plasma glucose concentration > 7.0 mmol/l (whole blood > 6.1mmol/l)
or
- two hour plasma glucose concentration > 11.1 mmol/l two hours after 75g anhydrous glucose in an oral glucose tolerance test (OGTT).
2. 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 or random values are not diagnostic the two hour value should be used
Classification and terms
- Insulin-dependent (IDDM) and non-insulin dependent diabetes (NIDDM) will be renamed Type 1 and Type 2 diabetes
- The terms Type 1 and Type 2 process will be introduced to describe the cause of insulin dependent and non-insulin dependent diabetes respectively. Both of these pathological processes will be clinically staged by the treatment that they need – from diet to insulin
- Impaired Glucose Tolerance (IGT)* is a stage of impaired glucose regulation (Fasting plasma glucose < 7.0 mmol/ and OGTT two hour value > 7.8mmol/l but < 11.1 mmol/l).
- Impaired Fasting Glycaemia (IFG)* has been introduced to classify individuals who have fasting glucose values above the normal range but below those diagnostic of diabetes. (Fasting plasma glucose > 6.1 mmol/l but < 7.0 mmol/l). Diabetes UK recommends that all those with IFG should have an OGTT to exclude the diagnosis of diabetes, and are actively managed with lifestyle advice.
- New: Gestational diabetes is retained but now encompasses the groups formerly classified as Gestational Impaired Glucose Tolerance (GIGT) and Gestational Diabetes Mellitus (GDM). Diabetes UK endorses the use of the WHO definition to allow for comparative studies. However, since glucose tolerance changes with the duration of pregnancy, the gestation at which the diagnosis was made should be recorded and, if made in the third trimester, the clinician should be cautious about the clinical implication of impaired glucose. Some concern has been expressed that the WHO level may be too tight for everyday clinical practice and the Diabetes Care Advisory Committee (DCAC) is currently consulting on revised recommendations. In the meantime, the DBA recommends that clinicians use their own clinical judgement when diagnosing Gestational diabetes in practice.
- It should be noted that children usually present with severe symptoms and diagnosis should then be based on a single raised blood glucose result, as above. Immediate referral to a Paediatric Diabetes Team should not be delayed.
A diagnosis of diabetes has important legal and medical implications for the patient and it is therefore essential to be secure in the diagnosis. A diagnosis should never be made on the basis of glycosuria or a stick reading of a finger prick blood glucose alone, although such tests may be useful for screening purposes. HbA1c measurement is also not currently recommended for the diagnosis of diabetes.
Diabetes UK recommends that the diagnosis is confirmed by a glucose measurement performed in an accredited laboratory on a venous plasma sample, although the WHO do give values for whole blood as well. This should mean that there is less need to perform oral glucose tolerance testing on the majority of the population, although in the elderly and some ethnic minority groups the fasting glucose may not be a reliable indicator of diabetes. For this group, and in the absence of symptoms of diabetes, Diabetes UK would recommend the use of a glucose tolerance test as the definitive second test.
Obviously there is some concern about the implications of these changes for diabetes care. The new criteria have simplified the diagnosis of diabetes and the ability to diagnose cardiovascular high risk cases in many people. Earlier diagnosis will increase the total number of people with diabetes, but if they are managed according to Diabetes UK guidelines, may of these new cases will be diet controlled. In the long term, complications should be lessened to the benefit of the individual and to the health service.
*IGT and IFG are not clinical entities in their own right, but rather risk categories for cardiovascular disease and/or future diabetes.