Association of the inflammation indicators with multiple system involved of immunoglobulin A vasculitis in children

Background Immunoglobulin A vasculitis (IgAV) is the most common childhood vasculitis, and involvement of multiple systems (gastrointestinal, joint, renal) may affect prognosis. Reliable biomarkers for predicting multi-system involvement are needed. Objective To investigate the association between routine inflammation-related laboratory indicators and multi-system involvement in children with IgAV. Methods A retrospective study included 657 children with IgAV diagnosed according to EULAR/PRINTO/PRES criteria. Patients were categorized into five mutually exclusive subgroups based on clinical phenotypes: skin only ( n = 75), gastrointestinal (GI, n = 96), joint ( n = 158), kidney ( n = 31), and multi-system ( n = 297) involvement. Laboratory parameters including white blood cell (WBC), neutrophils, platelets, neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), albumin, and D-dimer were compared across groups. Generalized additive models (GAM) and ROC curve analysis were used to determine optimal cut-off values for age and disease duration. Results Multi-system involvement was the most common phenotype (45.2%). Compared with other subgroups, multi-system involvement patients showed significantly higher WBC ( P = 0.032), neutrophils ( P = 0.001), platelets ( P = 0.002), NLR ( P = 0.001), PLR ( P = 0.002), and D-dimer, while albumin was lowest ( P < 0.001). Pairwise comparisons revealed that NLR and PLR elevations were most pronounced between multi-system and skin-only groups. GAM analysis identified 10 years as the optimal cut-off for onset age; children >10 years had significantly higher renal involvement rates (25.49% vs. 11.39%, P < 0.001) and higher NLR ( P = 0.019) than those ≤10 years. Multivariate logistic regression identified female sex (OR = 1.650, P = 0.038), onset age >10 years (OR = 2.160, P = 0.036), and longer disease duration (OR = 1.059, P = 0.037) as independent risk factors for renal involvement. Conclusion Elevated inflammatory markers including WBC, neutrophils, platelets, NLR, PLR, and D-dimer, as well as decreased albumin, are associated with multi-system involvement in children with IgAV, with the most pronounced differences observed between multi-system and skin-only groups. Onset age >10 years is associated with increased renal involvement risk. These routine laboratory indicators, interpreted in conjunction with age and disease duration, may aid in early risk stratification.