Background <p>CD163 is a surface marker expressed by M2c macrophages. This study aims to evaluate the level of urinary soluble CD163 (u-sCD163) in children with IgA vasculitis with nephritis (IgAVN) and its potential diagnostic value.</p> Methods <p>U-sCD163 was analyzed in 73 children with IgAVN who underwent a kidney biopsy, 37 children with IgA nephropathy and 50 normal controls. CD163 expression was analyzed by immunohistochemistry. Correlation analyses and inter-group comparison were performed to assess the association between u-sCD163 levels and clinicopathological features of IgAVN. The comparison of u-sCD163 levels before and after treatment was conducted.</p> Results <p>The level of u-sCD163 was significantly higher in children with IgAVN than healthy controls. Compared with grade II IgAVN subjects, u-sCD163 level was significantly elevated in grade III–IV subjects. There was no difference in u-sCD163 level between IgAVN and IgA nephropathy groups. There was no difference in serum CD163 level among different groups. In the IgAVN group, abundant CD163-positive cells were observed in glomeruli showing endocapillary proliferation, especially in areas of thrombosis and fibrinoid necrosis. In contrast, CD163-positive cells were scarce within cellular crescents, but increased in fibrocellular crescents. Levels of u-sCD163 showed a significant positive correlation with proportions of endocapillary proliferation, and moderately correlated with proteinuria, CD163 score of glomerular area, and weakly correlated with proportions of cellular crescents, D-dimer and fibrin degradation products (FDP). The level of u-sCD163 decreased significantly after treatment.</p> Conclusions <p>U-sCD163 emerges as a promising marker associated with endocapillary proliferation and coagulation in pediatric patients with IgAVN.</p> Graphical Abstract <p></p>