Reevaluation of urine C-peptide as measure of insulin secretion

• Published in: Diabetes (New York, N.Y.) Vol. 37; no. 9; pp. 1195 - 1201
• Main Authors: TILLIL, H, SHAPIRO, E. T, GIVEN, B. D, RUE, P, RUBENSTEIN, A. H, GALLOWAY, J. A, POLONSKY, K. S
• Format: Journal Article
• Language: English
• Published: Alexandria, VA American Diabetes Association 01-09-1988
• Subjects: Biological and medical sciences; C-Peptide - blood; C-Peptide - urine; Diabetes Mellitus, Type 2 - blood; Diabetes Mellitus, Type 2 - physiopathology; Diabetes Mellitus, Type 2 - urine; Diabetes. Impaired glucose tolerance; Endocrine pancreas. Apud cells (diseases); Endocrinopathies; Etiopathogenesis. Screening. Investigations. Target tissue resistance; Female; Humans; Insulin - blood; Insulin - metabolism; Insulin - urine; Insulin Secretion; Male; Medical sciences; Middle Aged; Monitoring, Physiologic - methods; Reference Values; Assay; Endocrinopathy; Human; Urine; Secretion; Non insulin dependent diabetes; Insulin; C-Peptide
• ISSN: 0012-1797; 1939-327X
• DOI: 10.2337/diab.37.9.1195

Urine C-peptide (UCP) has been proposed as a measure of insulin secretion, because insulin and C-peptide are consecreted in equimolar concentrations by the pancreatic beta-cell. The validity of this approach was tested by comparing insulin secretion rates, calculated by application of a two-compartmental analysis of peripheral C-peptide concentrations, with UCP excretion rates. Insulin secretion and UCP excretion with subjects on a mixed diet were simultaneously measured over a 24-h period in 13 patients with noninsulin-dependent diabetes mellitus and in 14 matched nondiabetic control subjects. The fraction of secreted C-peptide that was excreted in the urine (fractional C-peptide excretion) showed considerable intersubject variability in the diabetic (11.3 +/- 1.6%, range 3.9-20.8) and control (8.0 +/- 1.7%, range 1.1-27.9, P = .07) subjects (means +/- SE). UCP clearance demonstrated a similar degree of variability and was not significantly different (P = .07) between diabetic (23.8 +/- 3.0 ml/min) and control (16.5 +/- 2.7 ml/min) subjects. In control subjects, the 24-h insulin secretion rate correlated more closely with the fasting insulin secretion rate (r = .97, P = .0001), fasting C-peptide (r = .81, P = .0005), and fasting insulin (r = .80, P = .0005) concentrations than with the 24-h UCP excretion rate (r = .62, P = .02). Similar results were obtained in the diabetic patients.