Serum indoxyl sulfate as an early marker for detecting chronic cyclosporine nephrotoxicity

Background: Cyclosporine A (CsA) is an effective agent for frequently relapsing steroid‐dependent nephrotic syndrome (FR‐SDNS), but its use can also be complicated by renal toxicity. Because no biochemical markers from urine or blood samples have yet been established for detecting CsA‐induced renal injury to date, repeated renal biopsies are therefore required for all patients with long‐term CsA treatment. The purpose of the present study was therefore to detect early change of CsA nephropathy (CsAN) using blood samples. Methods: Several biochemical markers were analyzed in an attempt to examine the renal function in 24 patients with FR‐SDNS who had been treated with CsA. Those included serum cystatin C and indoxyl sulfate, as well as creatinine and β2‐microglobulin. Results: Renal biopsy findings indicated chronic CsAN in 13 of the 24 patients. Among those markers, only serum indoxyl sulfate was significantly elevated in patients with CsAN. Conclusions: It may be possible for measurement of serum indoxyl sulfate level to replace repeated renal biopsies in evaluation of chronic CsAN in pediatric patients with FR‐SDNS.