If there are two plus signs of protein in the urine routine, it indicates the presence of proteinuria. It is recommended to clarify the cause of proteinuria after further examination. The possible causes are: 1. Infectious proteinuria. When infection such as virus or bacteria occurs and causes glomerular destruction, damage to the filtration membrane can occur and lead to increased protein leakage, and then proteinuria will occur; accompanied by urinary tract irritation symptoms, such as frequent urination, urinary urgency and painful urination. Usually, infectious proteinuria is below two plus signs, and there are few proteinuria with more than two plus signs, which need to be further examined by culture of middle urine and 24-hour urine protein quantification, and also need to improve a series of tests such as kidney function. 2, renal proteinuria, when various diseases occur in the kidney, such as glomerulonephritis, acute glomerulonephritis, nephrotic syndrome or diabetic nephropathy, etc., can There is damage to the filtration membrane of the kidney resulting in a large amount of protein leakage. In this case, persistent proteinuria can occur, and further complementation tests, 24-hour urine protein quantification, renal function tests, and even renal puncture biopsy if necessary are needed to clarify the cause of proteinuria.