INS and rheumatoid arthritis: Thus, the impact of IR on the intact proinsulin-to-C-peptide ratio was higher in controls than in RA patients (6.23 (95% CI, 1.41 to 11.06) versus 0.43 (-0.86 to 1.71); P = 0.03); this association was not found in the split proinsulin/C-peptide ratio.