title: Validation of a single-sample urinary C-peptide creatinine ratio as a reproducible alternative to serum C-peptide in patients with Type 2 diabetes.
abstract: OBJECTIVE
  Serum C-peptide can be used in Type 2 diabetes as a measure of endogenous insulin secretion, but practicalities of collection limit its routine clinical use. Urine C-peptide creatinine ratio is a non-invasive alternative that is stable for at least 3 days at room temperature in boric acid preservative. We aimed to assess the utility of urine C-peptide creatinine ratio in individuals with Type 2 diabetes as an alternative to serum C-peptide.
  
  
  METHODS
  We assessed, in 77 individuals with Type 2 diabetes, the reproducibility of, and correlations between, fasting and postprandial urine C-peptide creatinine ratio and serum C-peptide, and the impact of renal impairment (estimated glomerular filtration rate < 60 ml min(-1) 1.73 m(-2)) on these correlations.
  
  
  RESULTS
  Urine C-peptide creatinine ratio was at least as reproducible as serum C-peptide [fasting coefficient of variation mean (95% CI): 28 (21-35)% vs. 38 (26-59)% and 2-h post-meal 26 (18-33)% vs. 27 (20-34)%. Urine C-peptide creatinine ratio 2 h post-meal was correlated with stimulated serum C-peptide, both the 2-h value (r = 0.64, P < 0.001) and the 2-h area under the C-peptide curve (r = 0.63, P < 0.001). The association seen was similar in patients with and without moderate renal impairment (P = 0.6).
  
  
  CONCLUSIONS
  In patients with Type 2 diabetes, a single urine C-peptide creatinine ratio is a stable, reproducible measure that is well correlated with serum C-peptide following meal stimulation, even if there is moderate renal impairment. Urine C-peptide creatinine ratio therefore has potential for use in clinical practice in the assessment of Type 2 diabetes.
authors: Peninsula NIHR Clinical Research Facility, Peninsula Medical School, University of Exeter, Exeter, UK. Andrew.Hattersley@pms.ac.uk
authors: P
authors: P
authors: Bowman
authors: T J
authors: TJ
authors: McDonald
authors: B M
authors: BM
authors: Shields
authors: B A
authors: BA
authors: Knight
authors: A T
authors: AT
authors: Hattersley
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000097:blood / Q000652:urine; D002096:C-Peptide / Q000097:blood / Q000652:urine*; D003404:Creatinine / Q000097:blood / Q000652:urine*; D003924:Diabetes Mellitus, Type 2 / Q000097:blood* / Q000652:urine*; D005215:Fasting; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D008297:Male; D019518:Postprandial Period; D011237:Predictive Value of Tests; D015203:Reproducibility of Results
chemical_list: D015415:Biomarkers; D002096:C-Peptide; D007328:Insulin; D003404:Creatinine