Allergic purpura (Henoch-Schonlein purpura, HSP) is a syndrome characterized by cutaneous purpura (rash), hemorrhagic gastroenteritis, arthritis, and renal damage, with diffuse necrotizing microangiitis as the underlying lesion. Renal damage (nephritis) is one of the most important manifestations and is the only chronic and distant symptom of the disease, which directly affects the long-term prognosis of the child.