Urine cystatin C as a biomarker of proximal tubular function immediately after kidney transplantation.

Background/aims: Clinical methods to predict allograft function soon after kidney transplantation are ineffective.

Methods: We analyzed urine cystatin C (CyC) in a prospective multicenter observational cohort study of deceased-donor kidney transplants to determine its peritransplant excretion pattern, utility for predicting delayed graft function (DGF) and association with 3-month graft function. Serial urine samples were collected for 2 days following transplant and analyzed blindly for CyC. We defined DGF as any hemodialysis in the first week after transplant, slow graft function (SGF) as a serum creatinine reduction < 70% by the first week and immediate graft function (IGF) as a reduction ≥ 70%.

Results: Of 91 recipients, 33 had DGF, 34 had SGF and 24 had IGF. Urine CyC/urine creatinine was highest in DGF for all time-points. The area under the curve (95% CI) for predicting DGF at 6 h was 0.69 (0.57-0.81) for urine CyC, 0.74 (0.62-0.86) for urine CyC/urine creatinine and 0.60 (0.45-0.75) for percent change in urine CyC. On the first postoperative day, urine CyC/urine creatinine and percent change in urine CyC were associated with 3-month graft function.

Conclusion: Urine CyC on the day after transplant differs between degrees of perioperative graft function and modestly corresponds with 3-month function.