Blood in your urine, called hematuria, most commonly comes from a urinary tract infection. But it can also signal kidney stones, an enlarged prostate, vigorous exercise, certain medications, or less commonly, cancer of the bladder or kidneys. Sometimes what looks like bloody urine turns out to be harmless discoloration from foods like beets. The cause matters, so even a single episode of visibly red or pink urine is worth getting checked out.
Visible Blood vs. Hidden Blood
There are two types of blood in urine. Gross hematuria is blood you can see, turning your urine pink, red, or cola-colored. Microscopic hematuria is invisible to the naked eye and only shows up on a lab test, defined as three or more red blood cells per high-power field under a microscope. Both types can share the same causes, but visible blood tends to carry a higher chance of something serious being involved.
The Most Common Causes
Urinary tract infections are the single most frequent reason for blood in urine. When bacteria infect the bladder or urethra, they inflame the lining and cause small amounts of bleeding. You’ll usually also have burning during urination, urgency, or pelvic pressure.
Kidney stones, bladder stones, or stones lodged in the tube connecting your kidney to your bladder are another major cause. As a stone moves, it scrapes and irritates the tissue lining your urinary tract. Mineral deposits can even erode through the inner surface of the kidney before they break free, which is why stones often produce blood before you feel any pain.
In men over 50, an enlarged prostate is a common culprit. As the prostate grows, it can compress the urethra and irritate surrounding tissue enough to produce bleeding. Chronic kidney disease, narrowing of the urethra, and menstrual blood mixing with a urine sample can also explain a positive test.
Exercise-Induced Hematuria
Intense physical activity, particularly long-distance running, can cause blood to appear in your urine even when nothing is wrong with your kidneys or bladder. This is sometimes called “runner’s hematuria.” It resolves on its own with rest, typically within 24 to 72 hours. If you notice pink or red urine after a hard workout, it’s worth confirming with a doctor that exercise is the actual explanation, but it’s a well-recognized and benign phenomenon.
Medications That Cause Bleeding
Several common drugs can lead to blood in your urine. Blood thinners like heparin, warfarin, and aspirin-type medications top the list because they reduce your blood’s ability to clot, making even minor irritation in the urinary tract produce visible bleeding. Penicillin-type antibiotics, sulfa drugs, and certain chemotherapy agents are also documented causes. NSAIDs like ibuprofen can contribute as well. Importantly, being on a blood thinner does not excuse you from evaluation. Current guidelines recommend the same workup for hematuria whether or not you take anticoagulants.
When It’s Not Actually Blood
Before you worry, consider what you ate or took recently. Beets, blackberries, and rhubarb can turn urine red or pink and have nothing to do with bleeding. The tuberculosis drug rifampin turns urine reddish-orange. Phenazopyridine, a common over-the-counter bladder pain reliever, does the same. Even some constipation medications containing senna can cause a color change. A simple urinalysis can tell you whether red blood cells are actually present.
The Cancer Question
This is likely what brought you here, and the numbers provide some perspective. Among people who show up with visible blood in their urine, roughly 17% are found to have bladder cancer, and about 2% have kidney cancer. Among those with only microscopic hematuria found on a lab test, the overall rate of any urinary tract cancer is around 5%. That means the large majority of hematuria cases are not cancer, but the risk is real enough that doctors take it seriously, especially in people over 40 who smoke or have smoked.
Painless gross hematuria is a particular red flag. When blood appears in your urine without any burning, urgency, or pain, it removes UTI and stones as obvious explanations and raises the likelihood of a tumor somewhere along the urinary tract. About 3% of all people tested for microscopic hematuria turn out to have cancer, so even trace amounts of blood found incidentally deserve follow-up.
What Happens During Evaluation
Your doctor will start with a urine sample examined under a microscope, a physical exam, blood pressure check, and a blood test to assess kidney function. From there, the workup depends on your risk level.
If you’re considered low risk (younger, no smoking history, small amount of blood on a single test), you’ll likely be asked to repeat a urinalysis in six months rather than undergo invasive testing right away. If blood persists on the repeat test, you get reclassified and evaluated more aggressively.
Intermediate-risk patients are typically recommended a cystoscopy, where a thin camera is passed through the urethra to visually inspect the bladder lining, along with an ultrasound of the kidneys. High-risk patients, such as older adults with a smoking history or visible blood, get cystoscopy plus a CT scan that images the entire urinary tract in detail.
Signs That Need Urgent Attention
Most hematuria can be evaluated through a scheduled appointment, but certain situations call for immediate care. Large blood clots in your urine can physically block urine from leaving the bladder, creating a painful and potentially dangerous obstruction. Heavy, sustained bleeding can also lead to significant blood loss. If you’re passing clots, unable to urinate, feeling lightheaded, or experiencing severe flank pain alongside bloody urine, those warrant a trip to the emergency room rather than waiting for a routine visit.