Serum IgA/C3 ratio and glomerular C3 staining predict progression of IgA nephropathy in children

Background: This retrospective study aimed to evaluate the significance of serum immunoglobulin A/complement 3 (IgA/C3) ratio and glomerular C3 staining at the onset of disease for predicting progression of IgA nephropathy in children. Methods: A total of 41 children with IgA nephropathy were allocated to two groups according to proteinuria (proteinuria <50 mg/kg/day group and proteinuria >= 50 mg/kg/day group) to compare their clinical data. Receiver operating characteristic (ROC) curves were used to evaluate the optimal cutoff value of serum IgA/C3 ratio in two groups. According to the optimal cutoff value of serum IgA/C3 ratio and glomerular C3 staining, the children were divided into four groups: Group A (serum IgA/C3 ratio <2.025 and glomerular C3 staining <2.0); Group B (serum IgA/C3 ratio >= 2.025 and glomerular C3 staining <2.0); Group C (serum IgA/C3 ratio <2.025 and glomerular C3 staining >= 2.0); and Group D (serum IgA/C3 ratio >= 2.025 and glomerular C3 staining >= 2.0). Then, the risk factors [including proteinuria and glomerular filtration rate (GFR) and pathological findings] were compared in these 4 groups at onset of IgA nephropathy. Results: Serum IgA/C3 ratio in the proteinuria <50 mg/kg/day group was significantly higher compared to the proteinuria >= 50 mg/kg/day group (P<0.01). According to ROC curves, the optimal cutoff value for the IgA/C3 ratio was 2.025 in two groups. At onset of IgA nephropathy, patients with IgA/C3 ratio <2.025 were predicted with nephrotic range proteinuria. When glomerular C3 staining was at the same level (glomerular C3 staining <2.0), GFR was significantly lower in group B (serum IgA/C3 ratio >= 2.025) compared with group A (serum IgA/C3 ratio <2.025). When serum IgA/C3 ratio was at the same level (serum IgA/C3 ratio <2.025), GFR was significantly lower in group C (glomerular C3 staining >= 2.0) compared with group A (glomerular C3 staining <2.0). Pathological findings and MEST (Oxford classification of IgA nephropathy) scores did not differ among the 4 groups at onset of the disease. Conclusions: Serum IgA/C3 ratio and glomerular C3 staining may be useful markers of the progression of IgA nephropathy in children, but not good markers for pathological findings at the onset of disease.