A urinary tract infection (UTI) is an infection in any part of the urinary system, typically caused by bacteria that multiply in the tract, most commonly affecting the bladder. A common symptom is the presence of blood in the urine, medically termed hematuria. If the blood is visible to the naked eye (gross hematuria), it appears pink, red, or dark brown. If the amount is too small to see and only detectable under a microscope, it is called microscopic hematuria.
The Source of Bleeding in a UTI
The bleeding during a UTI results from the body’s inflammatory response to the bacterial invasion. As bacteria colonize the urinary tract, they irritate the delicate lining of the urethra and bladder wall. This irritation triggers inflammation as the immune system attempts to fight the infection. The inflamed tissues become fragile, causing tiny blood vessels near the surface to leak red blood cells into the urine stream. The extent of this inflammation determines if the bleeding is visible (gross hematuria) or only detectable through testing.
Expected Duration After Starting Treatment
Once antibiotic treatment begins, the bacteria start to die off, and the inflammatory process begins to subside. For many patients, gross hematuria often decreases or disappears rapidly, typically within the first 24 to 48 hours of starting effective medication. This quick clearing of visible blood is a positive sign that the treatment is working and the acute irritation is resolving. While visible symptoms improve quickly, trace amounts of blood may persist longer. Studies indicate that microscopic hematuria may take a median of 66 days to completely resolve after a treated UTI, though this time frame varies widely. Factors such as the initial severity of the infection, adequate hydration, and adherence to the full course of antibiotics all influence the overall healing time.
When Bleeding Signals a Complication
The persistence or worsening of visible bleeding after starting treatment signals a potential complication. Bleeding that does not noticeably decrease after 72 hours of antibiotic treatment requires prompt medical reassessment. This lack of improvement suggests the infection is resistant to the medication or that a secondary issue is contributing to the hematuria.
A severe or increasing amount of gross hematuria, especially if accompanied by blood clots, is a significant warning sign. Clots may indicate a more severe source of bleeding or a blockage in the urinary tract that needs immediate attention. If bleeding is accompanied by systemic symptoms, the infection may have progressed beyond the bladder.
High fever, severe pain in the flank or side of the back, and persistent vomiting can signal pyelonephritis (a kidney infection), which requires a change in treatment and sometimes hospitalization. Persistent hematuria after the infection is cleared may also indicate an underlying urological issue unrelated to the UTI, such as a kidney stone or a need for further diagnostic testing. A full urological evaluation is necessary to confirm the source of persistent bleeding.