HbA1c in the diagnosis of diabetes mellitus

Chemical Pathology

Notes

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 (WHO guidance 2011)

Note that HbA1c and glucose should not be used simultaneously as these tests select for different populations of patients.

Please access the pathway for diagnosis of diabetes for further information (based on that issued to Leicester GP's).

An HbA1c of 48 mmol/mol is recommended as the cut point for diagnosing diabetes. A value of less than 48 mmol/mol does not exclude diabetes diagnosed using glucose tests.

Situations where HbA1c must not be used as the sole test to diagnose diabetes

• All symptomatic children and young people (<19 years of age)
• Symptoms suggesting Type 1 diabetes (any age).
• Short duration diabetes symptoms (<2 months)
• Patients at high risk of diabetes who are acutely ill.
• Taking medication that may cause rapid glucose rise e.g. steroids, antipsychotics.
• Acute pancreatic damage/pancreatic surgery.
• In pregnancy
• Presence of genetic, haematologic and illness-related factors that influence HbA1c and its measurement (see Annex 1 from WHO report)

Comments

• HbA1c should usually be measured on a laboratory venous blood sample.
• Point-of-care HbA1c should not be used for diagnosis unless the healthcare staff have been appropriately trained and the HbA1c 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 HbA1c.

Most patients

HbA1c ≥ 48 mmol/mol can be used to diagnose diabetes in most situations.

• In patients without symptoms but with an HbA1c ≥48 mmol/mol, repeat venous HbA1c in the same lab within 2 weeks (to confirm result and exclude any sampling/analytical error).
• If the second sample is <48 mmol/mol 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 ≥48 mmol/mol will suffice.

Patients whose HbA1c is <48 mmol/mol

• 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 do not provide specific guidance on HbA1c 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.
• High risk of diabetes and HbA1c 42 - 47 mmol/mol. Provide intensive lifestyle advice. Warn patients to report symptoms of diabetes. Monitor HbA1c at least annually.
• HbA1c values below 42 mmol/mol. Some of these patients may still be at risk of diabetes. If clinically at high risk, manage as above.

This guidance (excluding the pathway) is supported by the Association of British Clinical Diabetologists (ABCD), Association for Clinical Biochemistry (ACB), Community Diabetes Consultants (CDC), Diabetes UK, NHS Diabetes, Primary Care Diabetes Society (PCDS), Training, Research, and Education for Nurses in Diabetes UK (TREND UK).

Page last updated 03/06/2015