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 beta 2-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.