title: Levels of C-peptide, body mass index and age, and their usefulness in classification of diabetes in relation to autoimmunity, in adults with newly diagnosed diabetes in Kronoberg, Sweden.
abstract: OBJECTIVE
  C-peptide is a main outcome measure in treatment trials of diabetes. C-peptide also has a role in the classification of diabetes, which is often difficult in adults and this is also increasingly recognised in adolescents and elders.
  
  
  OBJECTIVE
  We aimed to describe the levels of C-peptide in relation to age and body mass index (BMI) in a large population-based cohort of adults with newly diagnosed diabetes and compare the capabilities of C-peptide, age and BMI to discriminate between autoimmune and non-autoimmune diabetes.
  
  
  METHODS
  Blood samples from 1180 patients were analysed regarding islet cell antibody, glutamic acid decarboxylase antibody and fasting C-peptide (FCP). Receiver operating characteristics (ROC) curves were analysed to check the ability of age, BMI and C-peptide to discriminate between autoantibody-positive (Ab(+)) and -negative (Ab(-)) diabetes.
  
  
  RESULTS
  Mean FCP was 0.73±0.5 (range 0.13-1.80) nmol/l in the Ab(+) and 1.42±0.9 (range 0.13-8.30) nmol/l in the Ab(-). FCP was 0.02 nmol/l higher per year increase in age at diagnosis of diabetes. Mean BMI was 26.0±4.8 (range 18.0-39.0) kg/m(2) in the Ab(+) and 28.9±5.3 (range 15.5-62.6) kg/m(2) in the Ab(-). FCP increased with age also within each BMI group. The highest area under the curve (AUC) in the ROC analysis was found for C-peptide, followed by age and BMI (0.78, 0.68 and 0.66 respectively).
  
  
  CONCLUSIONS
  At diagnosis of diabetes, C-peptide was superior to age and BMI in discriminating between autoimmune and non-autoimmune diabetes. C-peptide increased significantly with BMI and age, latter also within each BMI group. Most of the adults had normal or high levels of C-peptide at presentation of diabetes among the autoimmune patients.
authors.affiliation: Department of Internal Medicine, Central Hospital, Växjö, Kronoberg, Sweden. maria.thunander@ltkronoberg.se
authors.forename: Maria
authors.initials: M
authors.lastname: Thunander
authors.forename: Carina
authors.initials: C
authors.lastname: Törn
authors.forename: Christer
authors.initials: C
authors.lastname: Petersson
authors.forename: Birger
authors.initials: B
authors.lastname: Ossiansson
authors.forename: Jan
authors.initials: J
authors.lastname: Fornander
authors.forename: Mona
authors.initials: M
authors.lastname: Landin-Olsson
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging; D000704:Analysis of Variance; D019540:Area Under Curve; D001323:Autoantibodies / Q000097:blood*; D015551:Autoimmunity; D015415:Biomarkers / Q000097:blood; D015992:Body Mass Index; D002096:C-Peptide / Q000097:blood*; D002262:Carboxy-Lyases / Q000276:immunology; D003920:Diabetes Mellitus / Q000097:blood / Q000175:diagnosis* / Q000453:epidemiology / Q000276:immunology*; D003937:Diagnosis, Differential; D005215:Fasting / Q000097:blood; D005260:Female; D018698:Glutamic Acid / Q000276:immunology; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012372:ROC Curve; D018709:Statistics, Nonparametric; D013548:Sweden / Q000453:epidemiology
chemical_list: D001323:Autoantibodies; D015415:Biomarkers; D002096:C-Peptide; C024211:islet cell antibody; D018698:Glutamic Acid; D002262:Carboxy-Lyases