Home urine C-peptide creatinine ratio can be used to monitor islet transplant function.
Oram RA., Brooks AM., Forbes S., Eckoldt S., Smith RM., Choudhary P., Rosenthal MJ., Johnson P., Rutter MK., Burling KA., McDonald TJ., Shaw JAM., Hattersley AT.
OBJECTIVE: Islet graft function is defined by serum C-peptide in a standardized challenge test. We assessed whether urine C-peptide creatinine ratio (UCPCR) sent from home could provide a viable alternative. RESEARCH DESIGN AND METHODS: Seventeen islet recipients provided 90-min serum C-peptide (sCP90) and 120-min UCPCR (UCPCR120) samples during 68 interval posttransplant mixed-meal tolerance tests, also posting from home a 120-min postbreakfast UCPCR sample every 2 weeks. UCPCR was compared with a clinical score of islet function, derived from HbA1c and insulin dose. RESULTS: UCPCR120 and mean home postmeal UCPCR were strongly correlated with sCP90 (r(s) = 0.73, P < 0.001; and rs = 0.73, P < 0.01, respectively). Mean home UCPCR increased with clinical score (r(s) = 0.75; P < 0.001) and with graft function defined both by sCP90 >200 pmol/L and insulin independence. UCPCR cutoffs to detect insulin independence and poor graft function were sensitive and specific. CONCLUSIONS: Home UCPCR provides a valid measure of C-peptide production in islet transplant recipients.