Type 1 diabetes in adults: diagnosis and management

National Institute for Health and Care Excellence

Diagnosis and early care plan


  • Diagnose type 1 diabetes on clinical grounds in adults presenting with hyperglycaemia, bearing in mind that people with type 1 diabetes typically (but not always) have one or more of:
    • ketosis
    • rapid weight loss
    • age of onset below 50 years
    • BMI below 25 kg/m2
    • personal and/or family history of autoimmune disease
  • Do not discount a diagnosis of type 1 diabetes if an adult presents with a BMI of 25 kg/m2 or above or is aged 50 years or above
  • Do not measure C-peptide and/or diabetes-specific autoantibody titres routinely to confirm type 1 diabetes in adults
  • Consider further investigation in adults that involves measurement of C-peptide and/or diabetes-specific autoantibody titres if:
    • type 1 diabetes is suspected but the clinical presentation includes some atypical features (for example, age 50 years or above, BMI of 25 kg/m2 or above, slow evolution of hyperglycaemia or long prodrome) or
    • type 1 diabetes has been diagnosed and treatment started but there is a clinical suspicion that the person may have a monogenic form of diabetes, and C -peptide and/ or autoantibody testing may guide the use of genetic testing or
    • classification is uncertain, and confirming type 1 diabetes would have implications for availability of therapy (for example, continuous subcutaneous insulin infusion [CSII or 'insulin pump'] therapy)
  • When measuring C-peptide and/or diabetes-specific autoantibody titres, take into account that:
    • autoantibody tests have their lowest false negative rate at the time of diagnosis, and that the false negative rate rises thereafter
    • C-peptide has better discriminative value the longer the test is done after diagnosis
    • with autoantibody testing, carrying out tests for 2 different diabetes-specific autoantibodies, with at least 1 being positive, reduces the false negative rate

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