Blood in urine, known medically as hematuria, has a wide range of causes, from urinary tract infections and kidney stones to more serious conditions like bladder cancer. Sometimes the blood is visible, turning urine pink, red, or brown. Other times it’s only detectable under a microscope during a routine urine test. Either way, it signals that something along your urinary tract is leaking red blood cells, and finding the source matters.
Visible vs. Invisible Blood in Urine
There are two types. Gross hematuria is blood you can actually see. It only takes a tiny amount of blood to change your urine color, so even a faintly pink tinge counts. Microscopic hematuria, on the other hand, is blood found only through a urinalysis or when a lab technician examines your urine sample under a microscope. You’d never know it was there without testing.
Both types share the same list of possible causes. The difference is mainly in how they’re discovered and how urgently doctors investigate. Visible blood tends to prompt faster workups simply because it’s alarming and hard to ignore.
Urinary Tract Infections
UTIs are one of the most common reasons for blood in urine, especially in women. Bacteria enter through the urethra and multiply in the bladder, inflaming the bladder lining. That inflammation damages tiny blood vessels in the bladder wall, releasing red blood cells into the urine. Along with the bleeding, you’ll typically notice burning during urination, a frequent urge to go, and cloudy or strong-smelling urine.
If the infection travels upward to the kidneys, it becomes a more serious condition called pyelonephritis. Kidney infections can also happen when bacteria reach the kidneys through the bloodstream. These infections tend to cause flank pain, fever, chills, and nausea on top of the bloody urine, and they need prompt treatment with antibiotics to prevent lasting kidney damage.
Kidney Stones and Bladder Stones
Stones form when minerals in your urine crystallize and clump together, either in the kidneys or the bladder. As a stone moves through the urinary tract, its rough edges scrape against the delicate lining of the ureter or bladder, causing bleeding. The pain from a passing kidney stone is notoriously intense, usually hitting in waves along your side and lower back. But some stones sit quietly in the kidney for months, causing only microscopic hematuria with no pain at all.
Bladder stones develop when urine stays in the bladder too long, often because of an enlarged prostate or nerve damage that prevents complete emptying. They can cause intermittent bloody urine along with lower abdominal discomfort and difficulty urinating.
Enlarged Prostate
In men, a common cause of hematuria is benign prostatic hyperplasia, or an enlarged prostate. As the prostate grows, it compresses the urethra and can cause congestion in the blood vessels around the prostate and bladder neck. These congested, fragile vessels bleed more easily, sending blood into the urine. An enlarged prostate also makes it harder to fully empty the bladder, which can lead to secondary problems like infections or bladder stones that cause their own bleeding.
Because the same symptom can point to prostate cancer, doctors don’t assume an enlarged prostate is the explanation without further testing. Bloody urine in a man over 50 typically triggers imaging and possibly a direct look inside the bladder to rule out malignancy.
Bladder and Kidney Cancer
Painless blood in the urine, particularly in adults over 50, is one of the earliest warning signs of bladder cancer. It can also signal kidney cancer or, less commonly, cancer of the ureter or urethra. The bleeding often comes and goes, which can create a false sense of reassurance when the urine clears up on its own. That intermittent pattern is actually characteristic of urinary tract cancers and is exactly why even a single episode of visible hematuria in an older adult warrants investigation.
Cancer is not the most common cause of bloody urine overall, but it’s the most important one to rule out. The risk is higher in people who smoke, have a history of chemical exposure (particularly in the dye, rubber, or leather industries), or have undergone certain types of radiation therapy to the pelvis.
Kidney Disease and Glomerulonephritis
The kidneys filter blood through millions of tiny structures called glomeruli. When these filters become inflamed, a condition called glomerulonephritis, red blood cells leak through into the urine. This can happen on its own or as part of a systemic illness like lupus, diabetes, or certain infections. The hematuria from kidney disease is often microscopic and may be accompanied by protein in the urine, swelling in the legs or face, and high blood pressure.
Some inherited conditions also damage the kidneys’ filtering system. Sickle cell disease, for example, can cause hematuria by damaging blood vessels within the kidneys. Alport syndrome, a genetic condition affecting the kidney’s filtering membranes, frequently shows up as persistent microscopic hematuria starting in childhood.
Exercise-Induced Hematuria
Strenuous exercise, especially long-distance running, can cause blood to appear in the urine temporarily. One proposed mechanism involves the bladder bouncing against the pelvic bone during repetitive impact, sometimes called the “bladder slap” theory. Contact sports can also cause direct trauma to the kidneys or bladder. This type of hematuria is almost always microscopic and resolves on its own within 24 to 72 hours after stopping the activity.
If you notice blood in your urine after a hard workout, it’s worth rechecking after a few days of rest. Blood that persists beyond that window likely has a different cause.
Foods and Medications That Mimic Hematuria
Before assuming the worst, consider what you’ve eaten or taken recently. Beets, blackberries, and rhubarb can turn urine pink or red without any blood present at all. Certain medications do the same: rifampin (a tuberculosis drug) turns urine reddish-orange, phenazopyridine (a common UTI pain reliever) turns it bright orange to red, and laxatives containing senna can cause a similar color shift. None of these involve actual blood, and a simple urinalysis will confirm whether red blood cells are present.
Blood thinners won’t cause hematuria on their own, but if you have a small, otherwise unnoticeable source of bleeding somewhere in your urinary tract, anticoagulant medications can make it visible. In that situation, the blood thinner isn’t the root cause. It’s unmasking a problem that already existed.
How Doctors Find the Cause
The first step is a urinalysis to confirm that blood is actually present and not just a color change from food or medication. If red blood cells show up, your doctor will take a medical history and physical exam, then decide how aggressively to investigate based on your risk level.
Current guidelines from the American Urological Association use a risk-based approach. Younger patients with no other risk factors and a small amount of microscopic blood may simply have a repeat urinalysis in six months. Intermediate-risk patients typically get an ultrasound of the kidneys and a cystoscopy, a procedure where a thin camera is passed through the urethra to examine the bladder lining directly. High-risk patients, including older adults, smokers, and anyone with visible blood, generally get a CT scan along with cystoscopy to examine the entire urinary tract.
Blood tests may also be ordered to check kidney function, and in some cases a kidney biopsy is needed if glomerulonephritis is suspected.
When Blood in Urine Needs Urgent Attention
Most cases of hematuria are not emergencies. But certain accompanying symptoms change the picture. If you notice blood in your urine along with lightheadedness, inability to urinate, severe pain, or you’re passing large blood clots, that warrants immediate medical evaluation. These signs can indicate significant bleeding, a stone blocking urine flow, or a serious infection. A single painless episode of pink urine in an otherwise healthy person can usually wait for a scheduled appointment, but it shouldn’t be ignored entirely, especially if you’re over 40 or have risk factors for urinary tract cancers.