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Algorithm for the screening of diabetes mellitus using HbA1c

Circumstances when HbA1c must not be used as the sole test to diagnose diabetes

  • 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
  • Those taking medication that may cause rapid glucose rise e.g. steroids, antipsychotics
  • Acute pancreatic damage/pancreatic surgery
HbA1c reflects 2–3 month of hyperglycaemia and may not be elevated in these situations where blood glucose has risen rapidly
  • Altered haemoglobin (haemoglobinopathies)
Haemoglobinopathies may result in falsely increased or decreased HbA1c depending on assay
  • Altered glycation (alcoholism, chronic renal failure, aspirin)
Different glycation rates for haemoglobin
  • Anaemia, erythrocyte destruction e.g. splenectomy, antiretrovirals
New haemoglobin is unglycated
  • Assays e.g. hyperbilirubinaemia, alcoholism, large doses of aspirin, chronic opiate use, hypertriglyceridaemia
  • See Annex 1 WHO report
Interfere with some assay methods to falsely increase HbA1c
Caution: HbA1c should not be used to assess glycaemic status 6 weeks post partum—use OGTT HbA1c can also be elevated by:
  • Age. HbA1c is 4.5 mmol/mol higher at 70 than 40 years of age
  • Ethnicity. Afro-Caribbean and South Asians HbA1c is 4.5 mmol/mol higher than comparable Caucasians)

OGTT=oral glucose tolerance test.

NB. In above situations where HbA1c must not be used as the sole test to diagnose diabetes do an immediate quality-assured finger-prick capillary glucose test. If glucose is >11.0 mmol/l seek same-day specialist diabetes advice. For children and teenagers contact the specialist paediatric diabetes team same day. Send same day laboratory venous glucose, adding HbA1c to exclude stress hyperglycaemia and/or for baseline, but do not delay seeking advice while awaiting the result

WHO recommendation 2011

  • HbA1c can be used as a diagnostic test for providing:
    • stringent quality assurance tests are in place
    • assays are standardised to criteria aligned to the international reference values
    • there are no conditions present which precludes 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, which can still be diagnosed using glucose tests

The test

  • Analysis of venous HbA1c in UK laboratories participating in national quality assurance schemes currently fulfils WHO requirements. HbA1c should usually be measured on a laboratory venous blood sample. 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 laboratory quality assurance results. Finger prick tests must be confirmed by laboratory venous HbA1c in all patients

HbA1c≥48 mmol/mol (6.5%)

  • This can be used to diagnose diabetes in most situations. In patients without diabetes symptoms repeat the laboratory venous HbA1c. 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 symptoms develop. In symptomatic adults with relatively slow onset of symptoms a single result ≥48 mmol/mol will suffice

HbA1c <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 very high risk of diabetes. The use of such glucose tests is not recommended routinely in this situation
  • WHO did not provide specific guidance on HbA1c criteria for this 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 HbA1c 42–47 mmol/mol (6.0–6.4%)

  • Provide intensive lifestyle advice. Warn patients to report symptoms of diabetes. Monitor HbA1c annually

HbA1c <42 mmol/mol (6.0%)

  • These patients may still have high risk of diabetes. Review the patient’s personal risk and treat as ‘high risk of diabetes’ if clinically indicated

IDF definition of metabolic syndrome:

  • Central obesity (defined as waist circumference ≥94 cm for Europid men and ≥80 cm for Europid women, with ethnicity specific values for other groups) plus any two of the following four factors:
    • raised triglyceride level: ≥1.7 mmol/l, or specific treatment for this lipid abnormality
    • reduced high-density lipoprotein cholesterol: <1.03 mmol/l in males and <1.29 mmol/l in females, or specific treatment for this lipid abnormality
    • raised blood pressure: systolic BP ≥130 or diastolic BP ≥85 mm Hg, or treatment of previously diagnosed hypertension
    • raised fasting plasma glucose: ≥5.6 mmol/l, or previously diagnosed type 2 diabetes. If above 5.6 mmol/l, oral glucose tolerance test is strongly recommended but is not necessary to define presence of the syndrome

full guideline available from…


Welsh Endocrinology and Diabetes Society. Screening for diabetes mellitus using HbA1c.
First included: May 2017.