C-peptide determination in the choice of treatment in diabetes mellitus.

The predictive value of the intravenous glucagon test in assessing the requirement of insulin therapy in diabetes mellitus was evaluated in 105 adult diabetics. Basal and stimulated C-peptide concentrations and increments of C-peptide concentration were examined separately among newly and previously diagnosed diabetics. The poststimulatory C-peptide concentration of 0.6 nmol/l (Novo, antibody M 1230) proved to be the most reliable basis for the choice of therapy. Adequate therapy could have been assessed in 70 cases (67%) without glucagon stimulation. To derive maximal information of plasma C-peptide concentrations, a biphasic scheme of the use for C-peptide determinations and glucagon stimulation is presented. Basal and stimulated C-peptide levels of insulin-requiring diabetics correlated negatively with the duration of diabetes but they did not correlate with the relative body weights. Basal and stimulated C-peptide levels of non-insulin-requiring diabetics did not correlate with the duration of diabetes, but they correlated positively with the relative body weights.