C3 and purpura: We observed a consistent significant association between 12 risk factors and renal involvement in childhood HSP: gender, age, abdominal pain, gastrointestinal bleeding, severe bowel angina, persistent or relapse purpura, WBC > 15 × 109/L, platelet count > 500 × 109/L, elevated ASO, and decreased complement component 3 (C3; Table 3 and Figs 2–5).