Blood in the urine can indicate anything from a urinary tract infection to kidney stones to, less commonly, cancer of the bladder or kidneys. Most causes are treatable and not life-threatening, but visible blood in urine always warrants medical evaluation because the cause isn’t something you can determine on your own.
Sometimes you can see the blood yourself: urine that looks pink, red, or cola-colored. Other times, the blood is only detectable under a microscope during a routine urine test. Both forms matter, though visible blood is more strongly associated with serious conditions.
Visible vs. Invisible Blood
Doctors distinguish between two types. Visible blood (gross hematuria) is anything you can see with your own eyes, turning urine pink, red, or dark brown. It doesn’t take much blood to change the color. Even a small amount can make an entire toilet bowl look alarming.
Microscopic hematuria, on the other hand, is invisible. It’s typically discovered during a routine urinalysis, defined as three or more red blood cells per high-power field on a single urine sample. You’d never know it was there without testing. Both types can point to the same underlying causes, but visible blood carries a higher statistical likelihood of a serious diagnosis, which is why it usually triggers a more urgent workup.
The Most Common Causes
Urinary tract infections are one of the leading reasons for blood in urine, especially in women. Bacteria enter through the urethra and multiply in the bladder, causing inflammation that damages tiny blood vessels in the bladder lining. You’ll typically also notice burning during urination, a frequent urgent need to go, or cloudy, strong-smelling urine. UTIs are straightforward to treat with antibiotics.
Kidney and bladder stones are another frequent cause. Minerals in urine crystallize on the walls of the kidneys or bladder and gradually harden into stones. Small stones can pass without symptoms, but larger ones cause intense pain, especially when they move through the narrow tubes connecting your kidneys to your bladder. Stones can cause both visible and microscopic bleeding.
In men over 50, an enlarged prostate is a common culprit. As the prostate gland grows, it can press on the urethra and irritate surrounding tissue, leading to difficulty urinating, a persistent urge to go, and blood in the urine. Prostate infections (prostatitis) produce similar symptoms and can affect men at any age.
Vigorous exercise, particularly long-distance running, can cause temporary blood in the urine. The exact mechanism isn’t fully understood, but it’s thought to involve minor trauma to the bladder wall or increased blood flow through the kidneys during intense effort. Exercise-induced hematuria resolves with rest and doesn’t indicate underlying kidney or urinary tract disease. If the blood persists after a day or two of rest, something else is going on.
Less common causes include endometriosis, sexual activity, recent urinary tract procedures, and trauma to the kidneys or bladder.
When It Signals Something Serious
The concern most people have when they see blood in their urine is cancer, and it’s worth putting that risk in perspective. A large systematic review in European Urology found that among people with visible blood in the urine, about 17% were ultimately diagnosed with bladder cancer and roughly 2% with kidney cancer. For those with only microscopic blood, the rates were much lower: 3.3% for bladder cancer and under 1% for kidney cancer.
Those numbers mean the majority of people with blood in their urine do not have cancer. But they also mean the possibility is real enough that it can’t be ignored, especially for people with risk factors. Smoking is the single biggest modifiable risk factor for bladder and kidney cancer. Urologists specifically ask about smoking history, including how many years and how heavily, because it directly influences how aggressively they investigate.
Other serious causes include kidney diseases that damage the tiny filtering units (glomeruli) inside the kidneys, blood-clotting disorders like hemophilia, and sickle cell disease. Glomerulonephritis, a type of kidney inflammation, often shows up as microscopic hematuria discovered incidentally during lab work.
Things That Mimic Blood in Urine
Before assuming the worst, consider whether something you ate or took could be changing your urine color. Beets, blackberries, and rhubarb can all turn urine red or pink. Certain medications do the same: rifampin (a tuberculosis drug) turns urine reddish-orange, and phenazopyridine (a common over-the-counter bladder pain reliever) produces a vivid orange-red color. Laxatives containing senna can also cause color changes. None of these involve actual blood, and the color change stops when you stop consuming them.
If you’ve recently eaten beets and notice pink urine, wait a day or two. If the color clears, that was likely the explanation. If it doesn’t, or if you’re also experiencing pain, fever, or difficulty urinating, that points toward an actual medical cause.
How Doctors Figure Out the Cause
The evaluation starts with your history: your age, sex, smoking habits, medications, recent infections, and any symptoms accompanying the blood. Current guidelines from the American Urological Association use a risk-based approach. Your doctor assigns a risk level based on factors like how much blood was found, your age, and your smoking history.
Lower-risk patients, such as younger nonsmokers with only a few red blood cells on their urine test, may initially be evaluated with an ultrasound of the kidneys and bladder. Higher-risk patients, particularly older adults, heavy smokers, or those with visible blood, typically undergo imaging of the urinary tract (often a CT scan) along with cystoscopy, a procedure where a thin camera is threaded through the urethra to visually inspect the bladder lining.
If the initial evaluation doesn’t find a cause, follow-up testing is usually recommended. Blood in the urine that comes and goes can still reflect an underlying problem, even if the first round of tests looks normal.
Risk Factors That Increase Your Odds
Certain people are more likely to develop hematuria. You’re at higher risk if you:
- Smoke or have a history of smoking. Even a past smoking habit raises your risk of bladder and kidney cancer for years afterward.
- Take blood thinners, aspirin, or certain antibiotics. These medications can promote bleeding throughout the urinary tract. Blood thinners don’t cause hematuria on their own, but they can unmask bleeding from an existing problem.
- Have a history of kidney stones or an enlarged prostate. Both conditions tend to recur and can cause repeated episodes of blood in the urine.
- Do intense endurance exercise. Long-distance runners and other endurance athletes experience exercise-related hematuria more frequently, though it’s typically harmless.
- Recently had a bacterial or viral infection. Strep infections and hepatitis can both trigger kidney inflammation that leads to blood in the urine.
Symptoms That Need Urgent Attention
Most blood in the urine isn’t an emergency, but certain accompanying symptoms signal that you shouldn’t wait for a scheduled appointment. If you’re passing large blood clots, if you can’t urinate at all despite feeling the urge, or if you have severe flank or abdominal pain along with bloody urine, those situations need prompt medical attention. Fever combined with bloody urine can indicate a kidney infection that needs treatment quickly to prevent it from spreading to the bloodstream.
Painless visible blood in the urine is sometimes treated casually because it doesn’t hurt, but it’s actually more concerning than painful hematuria in some ways. Kidney stones and UTIs hurt, giving you a clear reason to seek care. Painless bleeding, on the other hand, is the hallmark presentation of bladder cancer. That doesn’t mean painless blood always equals cancer, but it does mean it shouldn’t be dismissed just because nothing else feels wrong.