title: Urine C-peptide creatinine ratio can be used to assess insulin resistance and insulin production in people without diabetes: an observational study.
abstract: OBJECTIVE
  The current assessment of insulin resistance (IR) in epidemiology studies relies on the blood measurement of C-peptide or insulin. A urine C-peptide creatinine ratio (UCPCR) can be posted from home unaided. It is validated against serum measures of the insulin in people with diabetes. We tested whether UCPCR could be a surrogate measure of IR by examining the correlation of UCPCR with serum insulin, C-peptide and HOMA2 (Homeostasis Model Assessment 2)-IR in participants without diabetes and with chronic kidney disease (CKD).
  
  
  METHODS
  Observational study.
  
  
  METHODS
  Single-centre clinical research facility.
  
  
  METHODS
  37 healthy volunteers and 30 patients with CKD (glomerular filtration rate 15-60) were recruited.
  Serum insulin, C-peptide and glucose at fasting (0), 30, 60, 90 and 120 min were measured during an oral glucose tolerance test (OGTT). Second-void fasting UCPCR and 120 min post-OGTT UCPCR were collected. HOMA2-IR was calculated using fasting insulin and glucose. The associations between UCPCR and serum measures were assessed using Spearman's correlations.
  
  
  RESULTS
  In healthy volunteers, fasting second-void UCPCR strongly correlated with serum insulin (rs=0.69, p<0.0001), C-peptide (rs=0.73, p<0.0001) and HOMA2-IR (rs=-0.69, p<0.0001). 120 min post-OGTT UCPCR correlated strongly with C-peptide and insulin area under the curve. In patients with CKD, UCPCR did not correlate with serum C-peptide, insulin or HOMA2-IR.
  
  
  CONCLUSIONS
  In participants with normal renal function, UCPCR may be a simple, practical method for the assessment of IR in epidemiology studies.
authors.affiliation: NIHR Exeter Clinical Research Facility, University of Exeter Medical School, Royal Devon & Exeter NHS Foundation Trust, Exeter, UK.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Oram
authors.forename: Andrew
authors.initials: A
authors.lastname: Rawlingson
authors.forename: Beverley M
authors.initials: BM
authors.lastname: Shields
authors.forename: Coralie
authors.initials: C
authors.lastname: Bingham
authors.forename: Rachel E J
authors.initials: RE
authors.lastname: Besser
authors.forename: Tim J
authors.initials: TJ
authors.lastname: McDonald
authors.forename: Bridget A
authors.initials: BA
authors.lastname: Knight
authors.forename: Andrew T
authors.initials: AT
authors.lastname: Hattersley
keywords: Diabetes & Endocrinology; Statistics & Research Methods