Serum suPAR concentrations in patients with focal segmental glomerulosclerosis with end-stage renal disease

To the Editor: Huang et al.1 recently reported that plasma soluble urokinase receptor (suPAR) levels were significantly elevated in patients with focal segmental glomerulosclerosis (FSGS) compared to controls. This study confirmed that plasma suPAR levels are negatively correlated with estimated glomerular filtration rate (eGFR).2 Pretransplant serum suPAR concentration has been suggested as a predictor for posttransplant proteinuriarecurrence in patients with FSGS.3 However, these results may have been biased because the controls had higher eGFR.3 We questioned whether serum suPAR is a specific marker for FSGS recurrence risk after transplantation in patients on hemodialysis. We measured serum suPAR concentrations in eight chronic hemodialysis patients using a commercially available assay (Quantikine Human suPAR Immunoassay; R&D Diagnostics, Minneapolis, MN). Three patients had a history of biopsy-proven FSGS in their native kidney and recurrent FSGS in one or two kidney allografts, and five controls had non-FSGS chronic kidney disease (CKD). None of the patients had active infection or systemic malignancy. Serum suPAR levels were >3000 pg/ml in all patients, and were not higher in patients with FSGS compared to controls (Figure 1). Another recent study also concluded that serum suPAR concentration is not specific for FSGS and posttransplant recurrence.4 Of note, Huang et al.1 observed no differences in suPAR levels between patients with primary and secondary FSGS. These data indicate that suPAR measurement using the currently available assay is not helpful in the identification of patients with a high risk of posttransplant FSGS recurrence. Further studies are needed to identify potential specific pathogenic suPAR fragments in primary FSGS.