Blood clots in your urine point to bleeding somewhere along the urinary tract, from the kidneys down to the urethra. The causes range from common and relatively harmless conditions like an enlarged prostate or a urinary tract infection to more serious problems including bladder cancer and kidney disease. About one in five people who see a doctor for visible blood in their urine turn out to have a urological cancer, which is why the symptom always warrants medical evaluation, even when it seems to come and go “randomly.”
What the Clots Look Like and Why That Matters
Blood clots that form inside the urinary tract can take on different shapes depending on where the bleeding starts and how the clot travels. Small, jelly-like blobs often form in the bladder itself, where blood pools and coagulates before you void. Long, stringy, worm-like clots typically form inside narrow passages. In one documented case, a worm-shaped clot found in a collection bag was initially mistaken for a giant kidney parasite; analysis confirmed it was simply a blood clot that had been squeezed into that shape by the tube-like urethra.1Journal of Medical Case Reports. A single worm-like structure in a urine collection bag: a case report The color matters too. Bright red clots generally mean fresh, active bleeding closer to the bladder or urethra, while darker, tea-colored or brownish clots can suggest bleeding higher up in the kidneys or ureters, where blood has had more time to break down before reaching the bladder.
Your doctor can use microscopic analysis of urine to help distinguish between bleeding that originates in the kidney’s filtering units and bleeding from the bladder or prostate. When red blood cells appear misshapen under a microscope, that pattern suggests they squeezed through the kidney’s tiny filtering barriers. In one study examining kidney biopsies, patients with kidney-filtering diseases were far more likely to have these oddly shaped red blood cells, while patients with problems in the kidney’s drainage tubes showed microscopic blood but almost never the misshapen cells.2Nephrology Dialysis Transplantation. Urinalysis for the diagnosis of glomerulonephritis: role of dysmorphic red blood cells Knowing where the bleeding starts helps narrow down the list of possible causes.
The Most Common Causes
In a large diagnostic study of over 650 patients who had visible blood in their urine, the two most frequent diagnoses were an enlarged prostate and kidney stones, accounting for roughly a quarter and a fifth of all cases respectively.3Canadian Association of Radiologists Journal. The Diagnostic Yield of CT Urography in the Workup of Hematuria With Negative Cystoscopy These are worth understanding separately because they feel quite different and call for different responses.
An enlarged prostate, known as benign prostatic hyperplasia, is extremely common in men over 50. The swollen tissue develops extra blood vessels on its surface, and those vessels can rupture, sending blood into the urine. Sometimes the bleeding is severe enough to require treatment. One study found that a procedure to block the arteries feeding the prostate stopped the bleeding in over 90% of patients who had been dealing with repeated episodes of gross hematuria, and none of them needed further blood transfusions afterward.4PubMed. Prostatic Artery Embolization in Nonindex Benign Prostatic Hyperplasia Patients: Single-center Outcomes for Urinary Retention and Gross Prostatic Hematuria
Kidney stones can scrape the lining of the ureter or bladder as they move, causing bleeding and clots. This type of bleeding usually comes with sharp, cramping pain on one side of the lower back or abdomen, which helps distinguish it from other causes. Urinary tract infections can also cause bloody urine, particularly when the infection inflames the bladder lining enough to cause small amounts of bleeding. UTIs are among the most common causes of hematuria in younger women.
Hemorrhagic Cystitis and Bladder Inflammation
A more intense form of bladder inflammation called hemorrhagic cystitis deserves its own mention because it can produce alarming amounts of blood and clots. The most common triggers are not ordinary bacteria. Severe hemorrhagic cystitis typically arises from cancer chemotherapy drugs or radiation therapy aimed at tumors in the pelvic area.5PubMed Central. Hemorrhagic cystitis: A challenge to the urologist Certain chemotherapy agents, particularly cyclophosphamide, break down into byproducts that directly irritate the bladder wall. Radiation for cervical, prostate, or rectal cancers can damage the bladder’s blood vessels, sometimes causing bleeding that starts months or even years after treatment ends.
Infections can also cause hemorrhagic cystitis, but this happens mostly in people with weakened immune systems, such as bone marrow transplant recipients, where viral infections with BK virus or adenovirus are frequent culprits. If you are otherwise healthy and have not undergone chemotherapy or pelvic radiation, hemorrhagic cystitis is much less likely to explain your symptoms.
When Blood Thinners and Aspirin Are Involved
If you take a blood thinner like warfarin or an antiplatelet drug like aspirin, visible blood in your urine might seem like an obvious medication side effect. The reality is more complicated, and treating it as “just the medication” can be dangerous. One study of patients on anticoagulants or aspirin who developed visible hematuria found a treatable underlying condition about half the time, and roughly a quarter were diagnosed with a urinary tract tumor.6Urology. Clinical significance of gross hematuria and its evaluation in patients receiving anticoagulant and aspirin treatment Even among patients whose blood-thinning levels were excessively high, tumors were still found in about one in five.
A separate study confirmed that while the risk of a urological cause is somewhat lower when anticoagulation levels are very high, it never drops to zero.7PubMed Central. Macroscopic hematuria in patients on anticoagulation therapy The practical takeaway is clear: blood thinners can unmask bleeding from a problem that already exists rather than creating the problem from scratch. If you see blood in your urine while taking these medications, you still need a full workup. Skipping it because “it’s probably the warfarin” is one of the more common and consequential mistakes patients and sometimes even clinicians make.
Cancer as a Cause
Visible blood in the urine is one of the hallmark early symptoms of bladder cancer, and it is also a common sign of kidney cancer and cancers of the ureter. In a prospective study of patients presenting with gross hematuria, about one in five was found to have a bladder tumor.8European Urology. A Prospective Blinded Evaluation of Urine-DNA Testing for Detection of Urothelial Bladder Carcinoma in Patients with Gross Hematuria A separate study in a different population found a similar rate of about 20% for urological cancers overall among patients with gross hematuria, with the risk climbing in people over 60.9Pakistan Journal of Health Sciences. Urological Carcinomas in Patients Presented with Gross Hematuria
Kidney cancer can be particularly tricky to detect. One case report described a patient with persistent bloody urine who was found to have a kidney mass that did not show up on ultrasound or CT scan and was only caught on MRI.10PubMed Central. Persistent hematuria caused by renal cell carcinoma after aortic valve replacement and warfarin therapy The lesson is that if bleeding persists and initial imaging comes back clean, pushing for additional tests is reasonable.
Risk factors for urinary tract cancers include smoking, age over 50, occupational exposure to industrial chemicals, and a history of chronic bladder infections. Men are diagnosed with bladder cancer more often than women, though women who develop it tend to be diagnosed at a later stage, possibly because their symptoms are initially attributed to UTIs or menstruation.
Less Obvious Causes in Younger People
When blood clots show up in the urine of someone under 40, the list of likely causes shifts. Cancer becomes much less probable. In the CT urography study mentioned earlier, no upper urinary tract malignancy was found in any patient aged 50 or younger, and nearly 60% of younger patients had no identifiable cause at all.3Canadian Association of Radiologists Journal. The Diagnostic Yield of CT Urography in the Workup of Hematuria With Negative Cystoscopy That does not mean the bleeding is imaginary. It means the cause may be something standard imaging does not catch easily.
One underdiagnosed condition in younger people is nutcracker syndrome, where the left renal vein gets pinched between two arteries. The compression raises pressure in the vein, causing blood to leak into the urine. A case report described a 28-year-old woman who had recurring episodes of bloody urine with clots, initially treated as a UTI, before imaging eventually revealed the venous compression.11Radiology Case Reports. Beyond bladder clots: Unmasking nutcracker syndrome in refractory hematuria: A case report Nutcracker syndrome is more common in thin, tall individuals and tends to produce painless or mildly painful hematuria that comes and goes.
Sickle cell trait is another cause that gets overlooked. Most people with sickle cell trait live without symptoms, but the trait can cause a condition called renal papillary necrosis, where small areas of kidney tissue die and slough off, causing heavy bleeding. One reported case involved a 28-year-old woman with sickle cell trait who developed recurrent gross hematuria severe enough to require blood transfusions.12PubMed Central. Not so benign: Life-threatening hematuria from renal papillary necrosis in sickle cell trait If you carry sickle cell trait and are passing blood clots in your urine, make sure your doctor is aware of your hemoglobin status.
Vigorous exercise is another recognized trigger for hematuria, particularly in runners and endurance athletes. The bleeding usually resolves within a day or two of rest and does not produce large clots. If you notice bloody urine only after intense workouts and it clears quickly, exercise-induced hematuria is worth discussing with your doctor, though it still deserves at least one proper evaluation to rule out other causes.
When Clots Become an Emergency
Most episodes of bloody urine, while frightening, do not constitute an emergency. But there is a threshold where the bleeding becomes dangerous on its own, regardless of the underlying cause. When enough blood clots accumulate inside the bladder, they can physically block urine from draining. This condition, called bladder tamponade, is a painful urological emergency.13PubMed. Urinary bladder tamponade-an urological emergency The clots act like a plug, and the bladder keeps filling with urine it cannot release, causing intense lower abdominal pain, restlessness, and rising blood pressure. In rare cases, the pressure buildup can even lead to bladder rupture.14PubMed Central. A simple and effective method for bladder blood clot evacuation using hydrogen peroxide
If you are passing blood clots and then suddenly find you cannot urinate at all, or if you develop severe lower abdominal pain and feel an urgent but unsuccessful need to void, go to the emergency room. Treatment involves irrigating the bladder to flush out the clots, sometimes with a large catheter, sometimes with a specialized solution. In a study of 31 patients who underwent clot evacuation with a bladder washout technique, the procedure succeeded in clearing the clots in 27 cases; the remaining four required surgery.14PubMed Central. A simple and effective method for bladder blood clot evacuation using hydrogen peroxide
What Doctors Do to Find the Cause
The standard workup for visible hematuria typically includes a urine test, blood work, imaging of the kidneys and ureters, and a cystoscopy, which is a direct look inside the bladder with a small camera. CT urography is the most widely used imaging approach because it can detect kidney stones, tumors, and structural abnormalities in a single scan. Cystoscopy adds the ability to see the bladder lining directly, which is essential for catching flat tumors that imaging can miss.
Even with this full workup, a cause is not always found. In the large CT urography study, no diagnosis was reached in 41% of patients overall and 58% of those under 50.3Canadian Association of Radiologists Journal. The Diagnostic Yield of CT Urography in the Workup of Hematuria With Negative Cystoscopy That high rate of unexplained hematuria is frustrating for patients, but it is actually somewhat reassuring: it means serious pathology has been ruled out, at least for the moment. Guidelines generally recommend follow-up urine tests over the next year or two, with repeat imaging if the bleeding comes back.
Newer urine-based DNA tests show promise for improving detection of bladder cancer without invasive procedures. One prospective evaluation found that a urine-DNA test detected bladder tumors with 97% sensitivity among patients with visible hematuria, meaning it caught nearly all the cancers that were present.8European Urology. A Prospective Blinded Evaluation of Urine-DNA Testing for Detection of Urothelial Bladder Carcinoma in Patients with Gross Hematuria The trade-off was a fair number of false positives, so a positive result still requires cystoscopy to confirm. But a negative result was extremely reliable, with a 99% negative predictive value. Tests like these may eventually help reduce the number of unnecessary cystoscopies in lower-risk patients.
Menstruation, Dehydration, and Other Red Herrings
Before you panic, it is worth ruling out some common mix-ups. Menstrual blood can contaminate a urine sample and make it look bloody, which is one reason doctors ask about your menstrual cycle during evaluation. Severe dehydration can concentrate your urine to a dark amber or brownish color that looks alarming but contains no blood. Certain foods, particularly beets, blackberries, and rhubarb, can temporarily turn urine pink or red. Some medications, including rifampin and phenazopyridine, do the same.
The easy way to tell these apart from true hematuria: if you see actual clots, gelatinous masses, or tissue-like material in your urine, that is blood and not a food or color artifact. Clots do not come from beets. Similarly, if the color persists over multiple voids and across different days, it is far more likely to be genuine bleeding than a dietary quirk. A simple dipstick test at a doctor’s office can confirm whether red blood cells are present within minutes.
Age, Sex, and How Risk Differs
Your age and sex significantly shape which causes are most likely. In men over 50, an enlarged prostate and bladder cancer dominate the list. In women of reproductive age, UTIs and kidney stones are the leading causes, with endometriosis occasionally causing blood in the urine if tissue grows on or near the bladder. In children and young adults, kidney filtering diseases, sickle cell trait, and structural abnormalities like nutcracker syndrome are more common considerations.
Smoking is the single strongest modifiable risk factor for bladder cancer, responsible for roughly half of all cases. If you smoke and are passing blood clots in your urine, the urgency of getting evaluated goes up substantially. Former smokers remain at elevated risk for years after quitting, so a smoking history from decades ago is still relevant information for your doctor.
People taking direct oral anticoagulants, the newer blood thinners that have largely replaced warfarin, face a similar situation to warfarin users: the medication may lower the threshold at which an existing lesion bleeds enough to become visible, but it does not create the lesion. The full workup applies regardless of which anticoagulant you are on.