Diagnostic criteria for urinary tract infections must be based on a positive urine bacterial culture. If repeated quantitative cultures are negative, the presence of an active urinary tract infection may be considered absent. However, the results of urine bacterial culture should also be judged in conjunction with clinical manifestations. False-negative results can occur in the following cases: 1. The patient has used antibacterial drugs within the last 2 weeks. 2. The urine stays in the bladder for a short time, less than 6 hours, and the bacteria do not have enough time to multiply. This is more obvious in patients with symptoms of frequent and urgent urination. 3, Drinking too much water dilutes the bacterial urine. 4, The foci of bacterial infection are not accessible to the urinary tract. For example, in the early stage of hemorrhagic pyelonephritis or urinary tract obstruction, the patient has obvious symptoms of urinary tract infection, but the urine bacterial culture is negative. 5, urinary tract infection can be interstitial, such as chronic pyelonephritis without acute symptoms, some patients can have negative urine bacterial culture, but in acute attacks, urine bacterial culture is often positive. 6. L-type bacteria can only grow in hypertonic media and cannot be cultured in general media. It has been estimated that about 20% of patients with pyelonephritis who have negative urine bacterial cultures are related to L-type bacteria. Therefore, the reasons for negative urine culture should be analyzed and should be combined with clinical diagnosis and treatment. Negative urine culture does not exclude urinary tract infection.