Estimation of Insulin Secretion Rates from C-Peptide Levels: Comparison of Individual and Standard Kinetic Parameters for C-Peptide Clearance

Insulin secretion rates can be accurately estimated from plasma C-peptide levels with a two-compartment model for C-peptide distribution and degradation. In previous studies, the kinetic parameters of C-peptide clearance were derived in each subject from the decay curve observed after bolus intravenous injection of biosynthetic human C-peptide. To determine whether standard parameters for C-peptide clearance could be defined and used to calculate insulin secretion without obtaining a decay curve in each subject, we analyzed 200 decay curves of biosynthetic human C-peptide obtained in normal, obese, and non-insulindependent diabetes mellitus subjects studied in ourlaboratory. This analysis showed that the volume of distribution and kinetic parameters of C-peptide distribution and metabolism vary by