Blood in urine has a wide range of causes, from urinary tract infections and kidney stones to more serious conditions like bladder cancer. In many cases, the cause is benign and temporary, but visible blood in your urine always warrants medical evaluation. Even blood you can’t see, detected only on a urine test, can sometimes signal a problem that needs attention.
Two Types of Blood in Urine
Doctors distinguish between blood you can see and blood you can’t. Visible blood turns urine pink, red, or cola-colored and is called gross hematuria. Microscopic hematuria, on the other hand, is invisible to the naked eye and only shows up under a microscope during a routine urine test. The American Urological Association defines microscopic hematuria as three or more red blood cells per high-power field on urine microscopy.
Both types share many of the same causes, but visible blood is more likely to prompt an urgent workup because the underlying cause tends to be more clinically significant.
Urinary Tract Infections
UTIs are one of the most common reasons for blood in urine, especially in women. When bacteria infect the bladder lining, the resulting inflammation can cause small blood vessels to leak. Along with blood, you’ll typically notice frequent urination, a burning sensation when you pee, urgency, and discomfort in the lower abdomen. The blood usually clears once the infection is treated with antibiotics.
Kidney infections can also cause hematuria, often with more intense symptoms like fever, flank pain, and nausea. These are more serious than bladder infections and need prompt treatment.
Kidney Stones
Kidney stones are another leading cause. Pain with hematuria is the most common way stones present, and most patients with stones will have either visible or microscopic blood in their urine. The blood appears because a stone scrapes the lining of the ureter (the tube connecting the kidney to the bladder) as it moves. Small stones may pass with minimal symptoms, while larger ones can cause intense, wave-like pain in the back or side that radiates toward the groin.
The amount of blood you see doesn’t necessarily correspond to the size of the stone. A tiny stone can produce visible blood if it irritates the ureter in the right spot, while a larger stone lodged in the kidney may cause only microscopic bleeding.
Enlarged Prostate
In men over 50, an enlarged prostate gland is a frequent cause. As the prostate grows, it can compress the urethra and the blood vessels near the bladder neck, leading to blood in the urine. This is often accompanied by a weak urine stream, difficulty starting urination, or the need to urinate frequently at night. The condition itself is not cancerous, but the symptoms overlap enough with other problems that it still needs evaluation.
Bladder and Kidney Cancer
This is the cause most people worry about when they notice blood in their urine, and it’s the main reason doctors take hematuria seriously. The overall risk, however, depends heavily on your individual profile. Among patients evaluated for microscopic hematuria, the overall rate of finding any urinary tract tumor is about 3.1%. Urothelial cancers (bladder and upper urinary tract cancers) specifically account for roughly 1.5% of cases.
Risk isn’t evenly distributed. The AUA’s updated guidelines sort patients into low, intermediate, and high-risk categories based on factors like age, smoking history, and the degree of hematuria. In the low-risk group, the chance of urothelial cancer is just 0.2%. In the high-risk group, it rises to 3.8%. Smoking history, being over 50, and having visible blood all push you toward higher risk categories.
Painless blood in the urine, particularly in someone over 50 with a history of smoking, is the classic red flag. Unlike infections or stones, cancer-related bleeding often comes without any other symptoms, which is exactly why even a single episode of unexplained visible blood should be evaluated.
Kidney Disease
Blood can also enter the urine at the level of the kidney’s filtering units, called glomeruli. When the filtering barrier is damaged or dysfunctional, red blood cells squeeze through pores they normally can’t pass. Under a microscope, these cells look misshapen and irregular, a hallmark that helps doctors distinguish kidney disease from other causes.
Several conditions damage this barrier, including IgA nephropathy (one of the most common kidney diseases worldwide), lupus-related kidney inflammation, and inherited conditions like Alport syndrome. Glomerular bleeding often shows up alongside protein in the urine and may be accompanied by swelling in the legs, high blood pressure, or changes in urine output. If your doctor suspects a glomerular source, they’ll typically order blood tests for kidney function and may refer you to a nephrologist.
Exercise-Induced Hematuria
Intense exercise, particularly long-distance running, can cause blood in the urine that resolves within 24 to 48 hours of rest. Two mechanisms are at play. First, during prolonged exertion, blood flow to the kidneys drops as the body redirects circulation to working muscles. This temporary oxygen shortage can damage small blood vessels in the kidneys. Second, in runners specifically, the empty bladder wall can repeatedly slap against the bladder base with each stride, causing mechanical bleeding from the bladder neck.
Exercise-induced hematuria is typically harmless and clears quickly. But it’s considered a diagnosis of exclusion, meaning your doctor should rule out other causes before chalking it up to your workout.
Medications and Foods That Mimic Blood
Not every red urine sample actually contains blood. Beets, blackberries, and rhubarb can all turn urine red or pink. Several medications do the same: rifampin (a tuberculosis drug) produces a reddish-orange color, phenazopyridine (a common over-the-counter bladder pain reliever) turns urine bright orange, and laxatives containing senna can also cause a color shift. None of these involve actual blood cells in the urine.
Blood thinners don’t cause hematuria on their own, but they can unmask bleeding from an underlying problem that might have otherwise gone unnoticed. If you’re on a blood thinner and notice red urine, it still needs investigation for a source.
How Doctors Evaluate Hematuria
The workup depends on your risk level. A urinalysis confirms whether blood is actually present and can reveal signs of infection or kidney disease. From there, the evaluation typically involves some combination of imaging and direct visualization of the bladder.
For lower-risk patients, imaging with ultrasound or a CT scan may be sufficient to check for stones, masses, or structural problems. Higher-risk patients are more likely to need cystoscopy, where a thin camera is inserted through the urethra to examine the bladder lining directly. This is the most reliable way to detect or rule out bladder cancer.
The AUA’s 2025 updated guidelines use a revised risk stratification system to determine who needs what level of evaluation. Your age, sex, smoking history, the amount of blood detected, and whether you’ve had previous episodes all factor into this decision. If your initial evaluation is normal but hematuria persists, repeat testing over time is standard practice to catch anything that may have been too small to detect initially.