Urine C-peptide creatinine ratio is an alternative to stimulated serum C-peptide measurement in late-onset, insulin-treated diabetes

Diabet Med. 2011 Sep;28(9):1034-8. doi: 10.1111/j.1464-5491.2011.03272.x.

Abstract

Aims: Serum C-peptide measurement can assist clinical management of diabetes, but practicalities of collection limit widespread use. Urine C-peptide creatinine ratio may be a non-invasive practical alternative. The stability of C-peptide in urine allows outpatient or community testing. We aimed to assess how urine C-peptide creatinine ratio compared with serum C-peptide measurement during a mixed-meal tolerance test in individuals with late-onset, insulin-treated diabetes.

Methods: We correlated the gold standard of a stimulated serum C-peptide in a mixed-meal tolerance test with fasting and stimulated (mixed-meal tolerance test, standard home meal and largest home meal) urine C-peptide creatinine ratio in 51 subjects with insulin-treated diabetes (diagnosis after age 30 years, median age 66 years, median age at diagnosis 54, 42 with Type 2 diabetes, estimated glomerular filtration rate > 60 ml min(-1) 1.73 m(-2) ).

Results: Ninety-minute mixed-meal tolerance test serum C-peptide is correlated with mixed-meal tolerance test-stimulated urine C-peptide creatinine ratio (r = 0.82), urine C-peptide creatinine ratio after a standard breakfast at home (r = 0.73) and urine C-peptide creatinine ratio after largest home meal (r = 0.71). A stimulated (largest home meal) urine C-peptide creatinine ratio cut-off of 0.3 nmol/mmol had a 100% sensitivity and 96% specificity (area under receiver operating characteristic curve = 0.99) in identifying subjects without clinically significant endogenous insulin secretion (mixed-meal tolerance test-stimulated C-peptide < 0.2 nmol/l). In detecting a proposed serum C-peptide threshold for insulin requirement (stimulated serum C-peptide < 0.6 nmol/l), a stimulated (largest home meal) urine C-peptide creatinine ratio cut-off of 0.6 nmol/mmol had a sensitivity and specificity of 92%.

Conclusion: In patients with insulin-treated diabetes diagnosed after age 30 years, urine C-peptide creatinine ratio is well correlated with serum C-peptide and may provide a practical alternative measure to detect insulin deficiency for use in routine clinical practice.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Age of Onset
  • Aged
  • C-Peptide / blood
  • C-Peptide / urine*
  • Creatinine / urine*
  • Diabetes Mellitus, Type 1 / blood
  • Diabetes Mellitus, Type 1 / urine*
  • Diabetes Mellitus, Type 2 / blood
  • Diabetes Mellitus, Type 2 / urine*
  • Fasting
  • Female
  • Glucagon / blood
  • Glucagon / urine*
  • Glucose Tolerance Test
  • Glycated Hemoglobin A / urine*
  • Humans
  • Male
  • Middle Aged
  • Sensitivity and Specificity

Substances

  • C-Peptide
  • Glycated Hemoglobin A
  • hemoglobin A1c protein, human
  • Glucagon
  • Creatinine