Use of HbA 1c in the diagnosis of diabetes: The implementation of WHO guidance 2011

An expert group* has discussed the World Health Organization (WHO, 2011) report. The group agree that the WHO requirements are met in the UK (Box 1). HbA_1c is not suitable for use in everyone. Do not use HbA_1c to diagnose diabetes in pregnancy.

The test
Analysis of venous HbA_1c in UK laboratories participating in national quality assurance schemes currently fulfils WHO requirements. HbA_1c should usually be measured on a laboratory venous blood sample. Point-of-care HbA_1c should not be used for diagnosis unless the healthcare staff have been appropriately trained and the HbA_1c method used can demonstrate an internal quality control and external quality assessment performance that matches that of a laboratory method. Confirm a point-of-care diabetes diagnosis with laboratory venous HbA_1c.

Most patients
HbA_1c ≥48 mmol/mol (≥6.5%) can be used to diagnose diabetes in most situations. In patients without diabetes symptoms repeat venous HbA_1c in the same lab within 2 weeks. If the second sample is <48 mmol/mol (<6.5%) treat as high risk of diabetes and repeat the test in 6 months or sooner if diabetes symptoms develop. In symptomatic adults with relatively slow onset of symptoms a single result of ≥48 mmol/mol (≥6.5%) will suffice.

Situations where HbA_1c must not be used as the sole test to diagnose diabetes
HbA_1c reflects glycaemia over the preceding 2–3 months so may not be raised if blood glucose levels have risen rapidly. For example:

• All symptomatic children and young people.
• Symptoms suggesting type 1 diabetes (any age).
• Short duration diabetes symptoms.
• Patients at high risk of diabetes who are acutely ill.
• Taking medication that may cause rapid glucose rise, such as corticosteroids, antipsychotics.
• Acute pancreatic damage/pancreatic surgery.

Do an immediate quality-assured finger-prick capillary glucose test. Check blood/urine ketones if available. If glucose is >11.0 mmol/L seek same-day specialist diabetes advice. For children and teenagers phone the specialist paediatric diabetes team same day. Send same day laboratory venous glucose, adding HbA_1c to exclude stress hyperglycaemia and/or for baseline, but do not delay seeking advice while awaiting the result.

Presence of factors that influence HbA_1c and its measurement
See Annex 1 from the WHO (2011) report. Discuss the patient with your local laboratory or specialist diabetes team or use glucose testing. Factors include abnormal haemoglobins, anaemia, altered red blood cell lifespan.

Patients whose HbA_1c is <48 mmol/mol (<6.5%)
These patients may still fulfil WHO glucose criteria for the diagnosis of diabetes which can be used in patients with symptoms of diabetes or clinically at high risk of diabetes. Glucose tests are not recommended routinely in this situation.

WHO did not provide specific guidance on HbA_1c criteria for people at high risk of diabetes. Clinicians should consider the individual patient’s personal risk of diabetes and provide advice and monitoring accordingly. Pending NICE guidance (consultation document available at: http://bit.ly/uPRuC4), the expert group suggested using HbA_1c values below.

High risk of diabetes: HbA_1c 42–47 mmol/mol (6.0–6.4%)
Provide intensive lifestyle advice. Warn patients to report symptoms of diabetes. Monitor HbA_1c annually.

HbA_1c <42 mmol/mol (<6.0%)
Some of these patients may still be at risk of diabetes. If clinically at high risk manage as above pending NICE guidance. A detailed report will be available shortly.

This guidance is supported by the Association of British Clinical Diabetologists, Association for Clinical Biochemistry, Community Diabetes Consultants, Diabetes UK, NHS Diabetes, PCDS and Training Research and Education for Nurses in Diabetes UK.

*Expert Group
George Alberti, Barbara Bain, Ian Barnes, Julian Barth, Felix Burden, Fiona Campbell, Marie Cummins, Melanie Davies, Alison Daykin, Jane French, Roger Gadsby, Geoffrey Gill, Martin Hadley-Brown, Rowan Hillson (Chair), Richard Holt, Garry John, Brian Karet, Kamlesh Khunti, Eric Kilpatrick, Elizabeth Lynam, Sally Marshall, John McKnight, Nathan Moore, Anna Morton, Simon O’Neill, June James, Maurice O’Kane, Naveed Sattar, Robert Sheriff, Nicola Strother-Smith, Annette Thomas, Chris Walton, Nick Wareham, Heather White, Peter Winocour.