Acute T-Cell Rejection after Living-Donor Kidney Transplantation: Monitoring with Urinary Presepsin.

Rejection remains a major complication after kidney transplantation, yet biopsy carries risks and delays. Therefore, non-invasive biomarkers are needed to monitor rejection. The patient was a 27-year-old man who was diagnosed with focal segmental glomerulosclerosis one year earlier. His renal function gradually deteriorated, and he was referred to our hospital for living-donor kidney transplantation, which was performed with his mother as the ABO-compatible donor. A standard immunosuppressive protocol was administered with steroids, basiliximab, mycophenolate mofetil (MMF), and tacrolimus. On postoperative day 5, he contracted COVID-19 and was treated with molnupiravir; however, antigen positivity persisted, leading to a reduction in MMF. The serum creatinine level reached a minimum of 2.41 mg/dL on postoperative day 7 but subsequently rose to 5.86 mg/dL. An episode biopsy revealed acute T cell-mediated rejection (TCMR). He was treated with steroid pulse therapy and anti-thymocyte globulin, after which his renal function stabilized. Protocol biopsies at three months and one year also demonstrated improvements in TCMR. Urinary presepsin levels at the time of TCMR and at the three-month and one-year protocol biopsies were 13,075, 1,332, and 680 ng/g creatinine, respectively, correlating with changes in renal function and histological findings. This case suggests that urinary presepsin may be a valuable noninvasive biomarker for monitoring disease activity in TCMR.