There are many reasons for producing urine protein, which can be generally divided into the following four categories. I. Physiological proteinuria. Most of them have no organic lesions, and are commonly found in the following two conditions: functional proteinuria and postural proteinuria. Functional proteinuria is often caused by stressful conditions such as strenuous exercise, fever, and stress, resulting in transient proteinuria, mostly in adolescents; postural proteinuria is common in adolescents during puberty, and proteinuria occurs in upright and anterior convex spine postures, and disappears when lying down. Second, glomerular proteinuria. Proteinuria is caused by damage to the glomerular filtration membrane and increased permeability, resulting in the filtration of plasma protein and exceeding the reabsorption capacity of the renal tubules. C. Tubular proteinuria. When renal tubular structure or function is damaged, renal tubular reabsorption of normally filtered small molecular weight protein is impaired, resulting in protein excretion from the urine. IV. Overflow proteinuria. Proteinuria caused by an abnormal increase in small molecular weight proteins in the blood, such as light chain protein, hemoglobin and myoglobin in multiple myeloma, which are filtered out from the glomerulus beyond the renal tubular reabsorption threshold.