Blood in your urine, called hematuria, is a signal that something is irritating or damaging your urinary tract somewhere between your kidneys and the opening where urine leaves your body. The cause can range from something as minor as intense exercise to something as serious as bladder cancer. Most of the time, it turns out to be an infection or another treatable condition, but it always warrants a medical evaluation because color alone can’t tell you the cause.
Visible vs. Invisible Blood
Blood in urine shows up in two forms. Visible hematuria turns your toilet water pink, red, or cola-colored, and even a tiny amount of blood can change the color noticeably. Microscopic hematuria, on the other hand, is invisible to the naked eye and only shows up under a microscope during a routine urinalysis. The clinical threshold is three or more red blood cells per high-power field on a single properly collected urine sample, according to American Urological Association guidelines.
Both types matter. Visible blood tends to prompt faster evaluation because it’s alarming, but microscopic blood found on a routine test can be just as significant. The key difference is that visible blood is more strongly associated with urinary tract cancers, while microscopic blood is more often linked to kidney filtering problems or low-grade infections.
The Most Common Causes
Infections
Urinary tract infections are the single most frequent reason for blood in urine, especially in women. Bacteria enter the urethra and multiply in the bladder, causing inflammation that damages the bladder lining enough to release blood. Kidney infections, where bacteria travel up to the kidneys, can also cause bloody urine along with fever, flank pain, and feeling generally unwell. In men, infection of the prostate gland produces similar symptoms.
Stones
Kidney and bladder stones form when minerals in urine crystallize over time into hard deposits. As stones move through the urinary tract, they scrape tissue and cause bleeding. The pain from a passing stone is typically severe and comes in waves, concentrated in the back or side, and blood in the urine alongside that kind of pain is a strong clue that a stone is the culprit.
Enlarged Prostate
In men approaching middle age and beyond, the prostate gland commonly enlarges and presses on the urethra. This pressure can cause blood in the urine along with a weak stream, difficulty starting urination, or feeling like the bladder never fully empties.
Exercise
Strenuous physical activity, particularly long-distance running and contact sports like football, can trigger blood in the urine. The exact mechanism isn’t fully understood, but it likely involves repeated impact on the bladder 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 blood persists after a day or two of rest, something else is going on.
Kidney Disease
When the tiny filtering units in the kidneys become inflamed, a condition called glomerulonephritis, blood cells leak into the urine. This type of bleeding is often microscopic and may be the first sign of kidney disease related to diabetes or autoimmune conditions. Under a microscope, blood cells from the kidney filters look distorted and misshapen because they’ve been squeezed through damaged tissue, while blood from the bladder or ureters looks like normal round red blood cells. This distinction helps doctors pinpoint where the bleeding originates.
Cancer
Visible blood in the urine, particularly when painless, can signal bladder, kidney, or prostate cancer. A large review of nearly 230,000 patients published in European Urology found that about 17% of people with visible hematuria were diagnosed with bladder cancer, and about 2% had kidney cancer. Those numbers are high enough that painless visible blood in the urine is never something to wait on, especially for people over 50 or those who smoke.
Medications
Blood thinners, aspirin, and certain antibiotics like penicillin can cause genuine bleeding into the urine. If you’re taking any of these medications and notice blood, your doctor needs to know, but being on a blood thinner doesn’t automatically explain the bleeding. It still needs to be investigated.
Things That Look Like Blood but Aren’t
Before assuming the worst, consider what you’ve eaten or taken recently. Beets, blackberries, and rhubarb can turn urine pink or red. Certain medications also change urine color without causing actual bleeding: rifampin (used for tuberculosis) turns urine reddish-orange, phenazopyridine (a common bladder pain reliever) makes it bright orange, and laxatives containing senna can shift the color as well. A simple urinalysis will confirm whether there are actual red blood cells present or just pigment.
How the Cause Gets Identified
The evaluation depends on how likely your doctor thinks something serious could be going on. Doctors now use a risk-based approach that considers your age, smoking history, the amount of blood, and whether you have other symptoms.
For people at low risk, such as younger patients with a small amount of microscopic blood and no other concerning features, the recommendation is often to repeat the urinalysis in six months rather than immediately pursue invasive testing. If the blood is gone on recheck, no further workup is needed.
For people at intermediate risk, the standard evaluation includes an ultrasound of the kidneys and a cystoscopy. A cystoscopy involves passing a thin, flexible camera through the urethra into the bladder. The procedure typically takes five to ten minutes, uses numbing gel rather than general anesthesia, and causes mild burning with urination for a day or two afterward. It’s uncomfortable but usually tolerable.
For people at high risk, typically older adults, heavy smokers, or those with large amounts of visible blood, the workup adds a CT urogram. This specialized scan with contrast dye creates detailed images of the kidneys, ureters, and bladder. Cystoscopy is still performed because imaging alone can miss small bladder tumors.
What Your Age and Sex Mean for Risk
In women under 40, a urinary tract infection is by far the most common explanation. In men of the same age, stones and exercise are more typical causes. Inherited conditions like sickle cell disease or Alport syndrome, which damages the small blood vessels in the kidneys, can cause hematuria at any age, including childhood.
After age 50, the calculus shifts. Cancer risk rises substantially, particularly for men and for anyone who has smoked. An enlarged prostate becomes an increasingly common explanation in men. Kidney disease tied to long-standing diabetes or high blood pressure also becomes more prevalent. This is why the same symptom, blood in the urine, gets a more aggressive workup in a 60-year-old than in a 25-year-old.
Symptoms That Need Prompt Attention
Any visible blood in the urine warrants a call to your doctor, even if it happens once and goes away. Hematuria that comes and goes is a hallmark of bladder cancer, so disappearing blood is not reassuring.
Certain accompanying symptoms raise the urgency. Blood clots in the urine, difficulty urinating or inability to urinate at all, severe flank or abdominal pain, fever, or unexplained weight loss all point toward conditions that need faster evaluation. If you’re passing clots large enough to block urine flow, that’s an emergency room situation.
Even without dramatic symptoms, don’t assume blood in your urine will sort itself out. The vast majority of causes are treatable, and the serious ones are most treatable when caught early.