There is no such thing as the most dangerous level of red blood cells in the urine, as long as the value of red blood cells in the urine exceeds the normal value, it is abnormal and dangerous. When performing routine urinalysis, the number of red blood cells per high power field of view in the urine of a normal person should be less than three. If it is more than three, it is abnormal and may be due to pathological factors. A high level of red blood cells in the urine indicates danger, but there is no such thing as the most dangerous level of red blood cells. The specific degree of danger should be judged in conjunction with the cause of the patient’s illness, clinical symptoms and other factors. High red blood cells in urine may be caused by acute glomerulonephritis, acute pyelonephritis, ureteral stone, bladder stone, bladder tumor, ureteral tumor and other diseases. Patients may experience symptoms such as hematuria under the naked eye and hematuria under the microscope as a result. Once the value of red blood cells in urine exceeds the normal range, it indicates a certain degree of danger, in which case, further examination can be conducted as prescribed by the doctor to clarify the cause.