Stimulated urine C-peptide creatinine ratio vs serum C-peptide level for monitoring of β-cell function in the first year after diagnosis of Type 1 diabetes

Aims To determine if urine C‐peptide/creatinine ratio is a useful tool for monitoring β‐cell function in new‐onset Type 1 diabetes. Methods Data were obtained from a prospective immunomodulation study in people with Type 1 diabetes ≤ 3 months from diagnosis, with a standard mixed‐meal tolerance test and measurement of urine C‐peptide/creatinine ratio carried out at 0, 3, 6, 9 and 12 months. The change in the insulin‐dose‐adjusted HbA1c level was also correlated with the change in serum/urine C‐peptide level during the 12‐month follow‐up period. Results A significant reduction in urine C‐peptide/creatinine ratio, measured after a mixed‐meal, was reached at 9 months (−45.4%), whilst the reduction in stimulated serum C‐peptide level reached significance after 3 months (−54.7%) in placebo‐treated participants. Neither change in stimulated serum C‐peptide nor change in urine C‐peptide level correlated with each other, and nor did change in insulin‐dose‐adjusted HbA1c level in the first 6 months, but all measures correlated significantly in the second half of the 12‐month follow‐up period. Conclusion Mixed‐meal‐stimulated urine C‐peptide/creatinine ratio was similar to, although less sensitive than, stimulated serum C‐peptide level in monitoring β‐cell function during the first year after diagnosis. Because the former is significantly less invasive, it warrants inclusion in further studies in Type 1 diabetes and may represent an attractive alternative outcome measure in cohort studies and in children. What's new? Stimulated urine C‐peptide/creatinine ratio can detect decline in β‐cell function in the first 12 months after diagnosis of Type 1 diabetes. Stimulated urine sampling represents an alternative, less invasive means of monitoring residual insulin production in prospective studies such as trials and cohort studies.