The most common cause of blood in urine is a urinary tract infection (UTI). While dozens of conditions can send red blood cells into your urine, infections of the bladder, kidney, or urethra account for more cases than any other single cause, particularly in women. Other frequent culprits include kidney stones, an enlarged prostate in older men, and, less commonly, bladder or kidney cancer.
Why UTIs Cause Bleeding
A UTI causes blood in urine because the bacteria physically damage the lining of your urinary tract. The most common species involved produces a toxin that punches tiny holes in the cells lining your bladder wall. Those holes destabilize and eventually rupture the cells, releasing both nutrients the bacteria feed on and red blood cells that end up in your urine. A similar process happens with kidney infections, where bacterial toxins destroy tissue and can cause the infection to spread deeper.
Blood in the urine is one of the hallmark symptoms of a bladder infection (cystitis), alongside painful urination, frequent urges to go, and lower abdominal pressure. The bleeding typically resolves once the infection is treated. If you notice pink, red, or cola-colored urine alongside these symptoms, an infection is the most likely explanation.
Kidney and Bladder Stones
Stones that form in the kidneys or bladder are the second major cause of bloody urine. As a stone moves through the narrow tubes of the urinary tract, it scrapes against the inner lining and causes small tears that bleed. The bleeding can be visible to the naked eye or detectable only under a microscope, depending on the size and location of the stone.
Stone-related hematuria usually comes with other unmistakable signs: intense, wave-like pain in your side or lower back, nausea, and sometimes an urgent need to urinate. The pain often shifts location as the stone travels. Unlike a UTI, stone-related bleeding tends to come and go as the stone moves, and it resolves once the stone passes or is removed.
Enlarged Prostate
In men over 50, a common and often overlooked cause of blood in urine is benign prostatic hyperplasia, or an enlarged prostate. As the prostate grows, it puts pressure on the urethra and can cause small blood vessels on its surface to become fragile and bleed. This type of hematuria is typically microscopic, meaning you won’t see it yourself, but it shows up on routine urine tests. It often appears alongside other prostate-related symptoms like a weak urine stream, difficulty starting urination, or getting up multiple times at night to use the bathroom.
Exercise-Related Hematuria
Strenuous physical activity can cause temporary blood in the urine even in completely healthy people. Researchers have identified multiple mechanisms behind this, and they fall into two broad categories: intensity-related and duration-related. High-intensity exercise can reduce blood flow to the kidneys, causing oxygen-deprived tissue to leak red blood cells. Impact sports like running may cause direct trauma to the bladder, especially when it’s relatively empty, as the bladder walls slap together with each stride. Dehydration during prolonged exercise concentrates the urine and makes any trace of blood more detectable.
Exercise-induced hematuria is generally harmless and clears within 24 to 72 hours. If it persists beyond that window, something else is likely going on.
When Blood in Urine Signals Cancer
This is the possibility most people are worried about when they search this topic, so here’s what the numbers actually show. Visible blood in the urine is the first sign in about 80% of bladder cancer cases. That sounds alarming, but it works the other direction too: the vast majority of people who see blood in their urine do not have cancer. Infections, stones, and other benign causes are far more common.
That said, certain factors raise the level of concern. Age is the biggest one. Adults over 40 with blood in their urine, especially those with a history of smoking or occupational exposure to industrial chemicals, are at higher risk for an underlying malignancy. Bladder cancer-related bleeding is typically painless and intermittent, which can actually make it easier to dismiss. The blood may appear one day, disappear for weeks, and return. That pattern of painless, on-and-off bleeding in someone over 40 is what prompts a more thorough workup.
Visible vs. Microscopic Blood
Blood in the urine comes in two forms. Gross hematuria is visible: your urine looks pink, red, or dark brown. Microscopic hematuria is invisible to you and only shows up when a urine sample is examined in a lab. The clinical threshold is three or more red blood cells per high-power microscope field in a properly collected sample, according to the American Urological Association.
One important detail: a urine dipstick test can show a positive result for blood, but that alone isn’t enough for a diagnosis. Dipstick tests can react to things other than red blood cells. A positive dipstick should always be confirmed with microscopic analysis of the actual urine sample before any further workup begins.
Foods and Medications That Mimic It
Before assuming the worst, consider what you’ve eaten or taken recently. Beets, blackberries, and rhubarb can all turn urine red or pink, a harmless phenomenon sometimes called “beeturia.” Several medications do the same thing. The tuberculosis drug rifampin turns urine reddish-orange. Phenazopyridine, a common over-the-counter medication for urinary tract pain, produces a vivid orange-red color. Even senna-based laxatives can cause a noticeable color shift. None of these involve actual blood, and the color change stops once the food or medication clears your system.
How It Gets Evaluated
The evaluation depends on whether the blood is visible or microscopic, your age, and your risk profile. For visible blood in the urine, most experts recommend a combination of a scope exam of the bladder (where a thin camera is inserted through the urethra) and imaging of the upper urinary tract, typically a CT scan with contrast that captures the kidneys, ureters, and bladder in multiple phases.
For microscopic hematuria, the approach is more graduated. People with a family history of kidney cancer or certain genetic tumor syndromes get imaging regardless. For others, the decision about how aggressively to investigate depends on factors like age, smoking history, and the degree of blood detected. A urine culture is usually the first step to rule out infection, since that’s the most common and most treatable cause.
Notably, specialized urine tests for cancer markers are not recommended as a routine part of the initial evaluation. They don’t reliably improve the accuracy of standard testing, and they can produce misleading results that lead to unnecessary procedures.