The diagnosis of acute nephritis is actually not difficult, focusing on the following key points: 1. A history of upper respiratory or skin infections prior to the onset of the disease. 2. Typical manifestations of acute nephritis syndrome, including hematuria, proteinuria, reduced urine output, edema, and elevated blood pressure. Among these, hematuria is the most important basis for diagnosing acute nephritis, which can be gross hematuria or microscopic hematuria, and proteinuria can be mild or severe. 3. During the acute phase, there can be an increase in anti-O and a decrease in serum complement C3 concentration. 4. It commonly affects adolescents and children. 5. Most cases improve or even recover after four to eight weeks of treatment.