Abstract: We appreciate the interest of Maas et al.1.Maas R.J. Wetzels J.F. Deegens J.K. Serum suPAR concentrations in patients with focal segmental glomerulosclerosis with end-stage renal disease.Kidney Int. 2013; 14: 47Google Scholar in our study on soluble urokinase receptor (suPAR) in focal segmental glomerulosclerosis (FSGS).2.Huang J. Liu G. Zhang Y.M. et al.Plasma soluble urokinase receptor levels are increased but do not distinguish primary from secondary focal segmental glomerulosclerosis.Kidney Int. 2013; 84: 366-372Abstract Full Text Full Text PDF PubMed Scopus (78) Google Scholar Maas et al. raised the point that the identification of pathogenic suPAR fragments in primary FSGS was needed.1.Maas R.J. Wetzels J.F. Deegens J.K. Serum suPAR concentrations in patients with focal segmental glomerulosclerosis with end-stage renal disease.Kidney Int. 2013; 14: 47Google Scholar We agreed with them, as suPAR detected by current commercial ELISA kits included various forms.3.Blasi F. Carmeliet P. uPAR: a versatile signalling orchestrator.Nat Rev Mol Cell Biol. 2002; 3: 932-943Crossref PubMed Scopus (1070) Google Scholar They also argued that the current suPAR measurement was not helpful in the identification of a high risk of post-transplant recurrence in patients with FSGS, as the suPAR level was elevated owing to decreased estimated glomerular filtration rate (eGFR). In our study, plasma suPAR was indeed negatively correlated with eGFR; however, after adjusting for renal function, a multivariate linear regression analysis indicated that the plasma suPAR levels of patients with primary FSGS were still significantly higher than those of patients with minimal change disease (P=0.01) or membranous nephropathy (P=0.003).2.Huang J. Liu G. Zhang Y.M. et al.Plasma soluble urokinase receptor levels are increased but do not distinguish primary from secondary focal segmental glomerulosclerosis.Kidney Int. 2013; 84: 366-372Abstract Full Text Full Text PDF PubMed Scopus (78) Google Scholar This suggested that the elevated suPAR level in primary FSGS was not merely attributed to decreased eGFR. In our study, the suPAR levels were not significantly different between patients with primary and secondary FSGS.2.Huang J. Liu G. Zhang Y.M. et al.Plasma soluble urokinase receptor levels are increased but do not distinguish primary from secondary focal segmental glomerulosclerosis.Kidney Int. 2013; 84: 366-372Abstract Full Text Full Text PDF PubMed Scopus (78) Google Scholar There might be two possibilities. First, it might be true that there is no difference between the two groups. However, the sample size of patients with secondary FSGS was relatively small, and thus a larger cohort of patients is needed for further investigation. Second, as the definition of secondary FSGS in our study was nondiffuse effacement of podocyte foot processes, misclassification of primary and secondary FSGS in some patients could not be fully excluded,4.Jefferson J.A. Shankland S.J. Has the circulating permeability factor in primary FSGS been found?.Kidney Int. 2013; 84: 235-238Abstract Full Text Full Text PDF PubMed Scopus (18) Google Scholar which also needs further investigation.