Allergic purpura nephritis is defined as the involvement of the renal parenchyma in the case of allergic purpura. It is one of the common causes of systemic disorders involving the kidneys. The disease has a tendency to be prolonged and is one of the causes of chronic renal failure. The specific antigen of the disease is unknown to date, and there is often a history of infection, food and drug allergy before the onset of the disease. (1) Skin: It is often the first symptom and typically manifests as purpura of varying size, slightly protruding from the skin surface, symmetrically distributed on the extensor side of the lower limbs, around the ankle joint, occasionally involving the buttocks and the whole body. In young children, it can be accompanied by angioneurotic edema on the back of hands and feet, around the eyes and scalp, and in elderly patients, the center of purpura lesions can be hemorrhagic necrosis or ulcerative changes. The skin purpura can occur repeatedly in batches. (2) Gastrointestinal symptoms: manifested as abdominal pain, sometimes with varying degrees of gastrointestinal bleeding, patients have black stools or bloody stools. Occasionally, it may cause intussusception, perforation and necrosis. (3) Joint symptoms: Some patients also have joint symptoms, mostly involving the knee and ankle joints, manifesting as joint pain or swelling. (4) Renal involvement: The incidence varies (20-90%) and occurs within 1 month after the skin lesion, with a peak occurrence on day 10-15 in particular. The clinical manifestations are hematuria (including visual hematuria) and proteinuria of varying degrees. Edema is generally not severe, and 20-40% have increased blood pressure. The treatment of this disease includes: 1. General treatment: In the acute stage, rest should be paid attention to, which is beneficial for skin and joint symptoms. Find out the suspected allergens and remove them as much as possible, such as removing and treating infected foci, stopping the use of suspected allergy-causing drugs and foods, etc. Gastrointestinal symptoms can be treated with antispasmodics, fasting and fluids if necessary, and close observation for gastrointestinal surgical complications (e.g. intussusception). The H2-blocker cimetidine is effective in controlling recurrent skin purpura and reducing renal injury. These drugs competitively antagonize histamine and improve vascular permeability to reduce edema and bleeding in skin mucosa and internal organs. Initially, 20mg/kg can be given intravenously for one week, and then 15-20mg/kg can be given orally in divided doses for 1-2 weeks. Adrenocorticotropic hormone: effective for relieving arthritis and gastrointestinal symptoms, can be applied for a short period of time, generally 1-2mg/Kg of prednisone daily in two oral doses for 7-14 days. 2. Clinically, for children with clear renal injury, a reasonable treatment plan and course of treatment should be formulated according to the severity of the injury. Commonly used drugs include adrenocorticotropic hormone, cyclophosphamide and other immunosuppressive drugs, anticoagulation (such as heparin) and anti-platelet aggregation agent (Pansentin) drugs.