The sudden appearance of blood in the urine is recommended to go to the nearest hospital for examination to clarify the specific cause. Possible causes: First, acute urinary tract infection. In this case, in addition to blood in urine, it can also be accompanied by symptoms such as frequent and urgent urination and painful urination. There may also be pain in the lower abdomen and lower back pain. It is necessary to take urine for routine urine test or urine culture test. If you can see an increase in white blood cells, red blood cells and bacteria, you can confirm the diagnosis of infection, and you need active anti-infection treatment. Secondly, if an older patient has sudden blood in the urine, you should also consider whether you have a tumor of the urinary tract. The pain is often not obvious at first, and it only appears as simple hematuria, so it is necessary to conduct ultrasound or CT examination of the urinary system to rule out the presence of tumors. Third, stones in the urinary system. Such as kidney stones, ureteral stones and bladder stones can appear hematuria, accompanied by pain in the area where the stones are located, such as back pain, abdominal pain, etc. The pain is often severe and requires ultrasound examination of the urinary system to confirm the diagnosis.