title: Practical Classification Guidelines for Diabetes in patients treated with insulin: a cross-sectional study of the accuracy of diabetes diagnosis.
abstract: BACKGROUND
  Differentiating between type 1 and type 2 diabetes is fundamental to ensuring appropriate management of patients, but can be challenging, especially when treating with insulin. The 2010 UK Practical Classification Guidelines for Diabetes were developed to help make the differentiation.
  
  
  OBJECTIVE
  To assess diagnostic accuracy of the UK guidelines against 'gold standard' definitions of type 1 and type 2 diabetes based on measured C-peptide levels.
  
  
  METHODS
  In total, 601 adults with insulin-treated diabetes and diabetes duration ≥5 years were recruited in Devon, Northamptonshire, and Leicestershire.
  
  
  METHODS
  Baseline information and home urine sample were collected. Urinary C-peptide creatinine ratio (UCPCR) measures endogenous insulin production. Gold standard type 1 diabetes was defined as continuous insulin treatment within 3 years of diagnosis and absolute insulin deficiency (UCPCR<0.2 nmol/mmol ≥5 years post-diagnosis); all others classed as having type 2 diabetes. Diagnostic performance of the clinical criteria was assessed and other criteria explored using receiver operating characteristic (ROC) curves.
  
  
  RESULTS
  UK guidelines correctly classified 86% of participants. Most misclassifications occurred in patients classed as having type 1 diabetes who had significant endogenous insulin levels (57 out of 601; 9%); most in those diagnosed ≥35 years and treated with insulin from diagnosis, where 37 out of 66 (56%) were misclassified. Time to insulin and age at diagnosis performed best in predicting long-term endogenous insulin production (ROC AUC = 0.904 and 0.871); BMI was a less strong predictor of diabetes type (AUC = 0.824).
  
  
  CONCLUSIONS
  Current UK guidelines provide a pragmatic clinical approach to classification reflecting long-term endogenous insulin production; caution is needed in older patients commencing insulin from diagnosis, where misclassification rates are increased.
authors.affiliation: NIHR clinician scientist and StR in endocrine and diabetes, and general internal medicine;
authors.forename: Suzy V
authors.initials: SV
authors.lastname: Hope
authors.affiliation: NIHR clinician scientist and StR in endocrine and diabetes, and general internal medicine;
authors.forename: Sophie
authors.initials: S
authors.lastname: Wienand-Barnett
authors.affiliation: NIHR clinician scientist and StR in endocrine and diabetes, and general internal medicine;
authors.forename: Maggie
authors.initials: M
authors.lastname: Shepherd
authors.affiliation: NIHR clinician scientist and StR in endocrine and diabetes, and general internal medicine;
authors.forename: Sophie M
authors.initials: SM
authors.lastname: King
authors.affiliation: Research and Development Unit, Northampton General Hospital, Northampton.
authors.forename: Charles
authors.initials: C
authors.lastname: Fox
authors.affiliation: Diabetes Research Centre, College of Medicine, Biological Sciences and Psychology, University of Leicester and the Leicester Diabetes Centre (Air Wing), Leicester General Hospital, Leicester.
authors.forename: Kamlesh
authors.initials: K
authors.lastname: Khunti
authors.affiliation: NIHR clinician scientist and StR in endocrine and diabetes, and general internal medicine;
authors.forename: Richard A
authors.initials: RA
authors.lastname: Oram
authors.affiliation: NIHR clinician scientist and StR in endocrine and diabetes, and general internal medicine;
authors.forename: Bea A
authors.initials: BA
authors.lastname: Knight
authors.affiliation: NIHR clinician scientist and StR in endocrine and diabetes, and general internal medicine;
authors.forename: Andrew T
authors.initials: AT
authors.lastname: Hattersley
authors.affiliation: NIHR clinician scientist and StR in endocrine and diabetes, and general internal medicine;
authors.forename: Angus G
authors.initials: AG
authors.lastname: Jones
authors.affiliation: University of Exeter Medical School and Royal Devon and Exeter NHS Foundation Trust, Exeter NIHR Clinical Research Facility, Barrack Road, Exeter.
authors.forename: Beverley M
authors.initials: BM
authors.lastname: Shields
mesh_terms: D015415:Biomarkers / Q000652:urine; D015992:Body Mass Index; D002096:C-Peptide / Q000652:urine*; D003430:Cross-Sectional Studies; D003922:Diabetes Mellitus, Type 1 / Q000175:diagnosis* / Q000453:epidemiology; D003924:Diabetes Mellitus, Type 2 / Q000175:diagnosis* / Q000453:epidemiology; D005260:Female; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D008297:Male; D017410:Practice Guidelines as Topic; D012372:ROC Curve; D015203:Reproducibility of Results; D006113:United Kingdom / Q000453:epidemiology
chemical_list: D015415:Biomarkers; D002096:C-Peptide; D007328:Insulin
keywords: C-peptide; diabetes mellitus; general practice; insulin-treated diabetes; type 1/type 2 classification; type 1/type 2 diagnosis