Blood is essential to human function, and we're used to seeing it after cuts and scrapes.
For long-distance runners, prolonged pounding of the pavement can sometimes cause blood to seep from the kidneys and bladder and appear in the urine immediately after exercising.

Known as “runner’s hematuria,” the condition is harmless and clears up on its own within hours or days after ceasing strenuous exercise. But Matthew Dunn, M.D., assistant professor of urology at the Keck School of Medicine, warns that any time blood appears in the urine, a person should consult a doctor to eliminate more serious potential causes.

“A runner should never attribute blood in the urine to runner’s hematuria unless their doctor has ruled out other things that could be causing it—because many of the other conditions that can cause it are potentially life-threatening,” Dunn says. “You need to do an imaging study of the kidneys and ureters and make sure it’s not being caused by kidney stones, tumors or other disease.”

When a patient appears with blood in the urine, a physician typically conducts a urinalysis to look for chemical and cellular clues that point to a cause. White blood cells and bacteria in the urine mean an infection is the most likely culprit and may need to be treated with an appropriate antibiotic.

For a patient definitively diagnosed with runner’s hematuria, Dunn adds that however unsettling the symptoms, they are transitory and harmless: “It’s definitely something you can live with.”