Blood clots in urine are a sign of significant bleeding somewhere in the urinary tract, and they always warrant medical evaluation. While the causes range from treatable infections and kidney stones to more serious conditions like bladder cancer, the presence of actual clots (as opposed to a pinkish tinge) means enough blood is accumulating to coagulate before it leaves the body. That distinction matters because it often points to a source of active or heavy bleeding that needs to be identified.
Why Blood Clots Form in Urine
Blood in urine, called hematuria, can be microscopic (only visible under a lab microscope) or gross (visible to the naked eye). When you see clots, you’re dealing with gross hematuria at a level where blood is pooling in the bladder long enough to clot. This can happen when a blood vessel in the kidney, ureter, bladder, prostate, or urethra is damaged, inflamed, or abnormally formed.
The shape of the clots can sometimes hint at where the bleeding originates. Long, thin, worm-like clots often form inside the ureters, the narrow tubes connecting the kidneys to the bladder, suggesting the bleeding source is higher up in the urinary tract. Rounder, more irregular clots tend to form in the bladder itself.
Most Common Causes in Men
Urinary Tract Infections and Prostate Infections
Infections in the bladder, kidney, urethra, or prostate can inflame tissue enough to cause bleeding. A kidney infection is more likely to produce clots because the bleeding has time to coagulate as it travels down to the bladder. You’ll typically also have fever, chills, painful urination, or an urgent need to go. Prostatitis, an inflammation of the prostate, can cause bloody urine along with pelvic pain and difficulty urinating.
Kidney and Bladder Stones
Hard mineral deposits can scrape and irritate the lining of the kidneys, ureters, or bladder as they shift or try to pass. This mechanical damage to delicate tissue produces bleeding that can be heavy enough to form clots. Stones often cause intense pain in the back or lower abdomen alongside the visible blood, though some stones bleed without much pain at all. Back or bladder pain that accompanies blood clots in urine is a classic stone presentation.
Enlarged Prostate (BPH)
Benign prostatic hyperplasia, the gradual enlargement of the prostate that affects most men as they age, is one of the more common causes of blood in male urine. As the prostate grows, it develops an increasingly rich blood supply. These new, fragile blood vessels can rupture and bleed into the urethra or bladder. A study of 166 men evaluated at a hematuria clinic found that BPH-related vascular enlargement was a frequent final diagnosis, though actual clot retention (where clots block urine flow) occurred in about 1% of those cases.
Bladder, Kidney, or Prostate Cancer
This is the cause most people fear, and it’s the main reason blood clots in urine should never be ignored. A population-based study of nearly 1,500 patients with visible blood in their urine found that about 11% had a malignant tumor. Bladder cancer was by far the most common, accounting for 9% of all cases, while kidney cancer was found in 1.3%. Among men specifically, bladder cancer rates were notably high. These cancers often cause painless bleeding, which is why the absence of pain doesn’t rule out something serious.
Blood-Thinning Medications
If you take anticoagulants or antiplatelet drugs (prescribed for heart conditions, stroke prevention, or blood clot disorders), your risk of urinary bleeding is substantially higher. One study found that over 76% of patients hospitalized for gross hematuria were taking blood thinners, and these patients required significantly more treatment to clear the bleeding. Blood thinners don’t cause the bleeding on their own; they amplify bleeding from an existing source that might otherwise go unnoticed. This means even if medication is contributing, there’s usually an underlying issue that still needs investigation.
Vigorous Exercise
Hard physical activity, particularly contact sports like football or endurance sports like marathon running, can cause blood in the urine. Contact sports may result in direct bladder trauma from impact, while the mechanism in distance running is less well understood. Exercise-induced hematuria is typically short-lived and resolves within 24 to 72 hours of rest. Persistent bleeding after exercise warrants the same workup as any other cause.
Less Common Causes
Kidney disease affecting the glomeruli (the filtering units inside the kidneys) can cause blood to leak into urine. Blood-clotting disorders like hemophilia or sickle cell disease also increase the risk. Trauma to the pelvis, urethra, or penis is another possible source, as are recent urinary tract procedures like catheterization or prostate surgery.
When Blood Clots Become an Emergency
The biggest immediate danger of blood clots in urine isn’t the bleeding itself but the possibility that clots block the flow of urine out of the bladder. This is called clot retention, and it’s a medical emergency. If clots accumulate faster than you can pass them, the bladder fills and you lose the ability to urinate. Symptoms include severe lower abdominal pain, a swollen lower belly, and an urgent but impossible need to urinate.
You should seek emergency care if you notice blood clots along with an inability to urinate, severe abdominal pain, fever and chills, or nausea and vomiting. These combinations suggest either a urinary tract obstruction or a serious infection that can become life-threatening without prompt treatment.
How Doctors Find the Source
The evaluation typically involves two main steps: imaging and direct visualization. A CT scan with contrast (called CT urography) is the standard for examining the kidneys, ureters, and bladder for stones, tumors, or structural problems. If you can’t have a CT with contrast due to kidney problems or allergies, an MRI or ultrasound combined with other imaging techniques can substitute.
Cystoscopy, where a small camera is inserted through the urethra to look directly inside the bladder, is the standard for checking the bladder lining for tumors, inflammation, or other abnormalities. The American Urological Association recommends cystoscopy even for microscopic blood in the urine, so it’s especially important when actual clots are present. A urine test and culture will also check for infection, and blood work may be drawn to evaluate kidney function and clotting ability.
What Treatment Looks Like
Treatment depends entirely on the underlying cause. An infection gets antibiotics. Stones may pass on their own with pain management and fluids, or they may need to be broken up or surgically removed. An enlarged prostate can be managed with medications that shrink prostate tissue and reduce its blood supply. Cancer requires its own treatment path depending on type and stage.
When clots are actively forming and blocking urine flow, the immediate priority is clearing them. This typically involves inserting a catheter into the bladder and manually flushing it with saline to break up and remove clots. If that isn’t enough, continuous bladder irrigation, a steady flow of saline through the catheter, keeps clots from re-forming. For bleeding that doesn’t respond to irrigation, options include medications that promote clotting, cauterization of the bleeding site through a scope, or in rare severe cases, procedures to block blood flow to the affected area.
The key takeaway is that blood clots in urine are not something to wait out or hope resolves on its own. Even a single episode of visible clots justifies a full urological workup, because the most dangerous causes, particularly bladder cancer, often present with painless bleeding that comes and goes. Early evaluation catches treatable problems before they progress.