Intended for healthcare professionals

Practice Rational Testing

Distinguishing between type 1 and type 2 diabetes

BMJ 2020; 370 doi: (Published 11 August 2020) Cite this as: BMJ 2020;370:m2998
  1. Alexandra E Butler, professor and principal investigator 1,
  2. David Misselbrook, associate professor of family medicine 2
  1. 1Diabetes Research Center, Qatar Biomedical Research Institute, Hamad Bin Khalifa University, Qatar Foundation, Doha, Qatar
  2. 2Department of Family Medicine, Royal College of Surgeons in Ireland - Bahrain, Adliya, Kingdom of Bahrain
  1. Correspondence to A E Butler abutler{at}

What you need to know

  • In patients with new onset hyperglycaemia where the type of diabetes is ambiguous, diabetes specific autoantibodies are the diagnostic test of choice to distinguish between type 1 and type 2 diabetes

  • Patients with newly diagnosed diabetes who are over 40 and respond well to oral anti-hyperglycaemic therapy do not need to undergo testing to distinguish between type 1 and type 2 diabetes

  • Glycated haemoglobin (HbA1c) is not recommended as a diagnostic test for patients with possible or suspected type 1 diabetes because it may not reflect a recent rapid rise in blood glucose and results take longer than with serum glucose testing

A 33 year old man with no notable medical history attends his general practitioner reporting two months of fatigue, with no other symptoms. His mother has hypothyroidism. His body mass index is 25 kg/m2 and he has a pulse rate of 72 beats/min and blood pressure 135/88 mmHg with no postural drop. Examination is unremarkable. A random blood glucose test shows 14 mmol/L (250 mg/dL). Urinalysis is normal. The next day the patient returns, and a repeat fasting glucose test finds 14 mmol/L.

This article is intended to help primary care doctors to differentiate between type 1 and type 2 diabetes when first diagnosing diabetes in a patient where the distinction is unclear.

Differentiating between type 1 and type 2 diabetes

For people who fit the classic pattern of type 2 diabetes (table 1), and where two glucose test results are in the diabetic range (box 1), no further testing is required for diagnosis, and management should follow current guidelines.1 Follow-up testing of glycated haemoglobin (HbA1c) is useful to assess glycaemia over time and to tailor treatment.1

View this table:
Table 1

Clinical features at presentation that help to distinguish type 1 and type 2 diabetes

Box 1

Criteria for the diagnosis of diabetes (all types) as determined by the World Health Organization and the American Diabetes Association17

  • Fasting plasma glucose (FPG) ≥7.0 mmol/L (126 mg/dL), or …

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