Blood in your urine, known medically as hematuria, signals that something is causing red blood cells to leak into your urinary tract. The cause ranges from something as common and treatable as a urinary tract infection to something that needs closer attention, like a kidney stone or, less often, cancer. Sometimes it’s visible to the naked eye, turning urine pink, red, or cola-colored. Other times it’s only detectable under a microscope during a routine test.
Visible vs. Invisible Blood
There are two types. Visible (gross) hematuria is the kind you can see in the toilet bowl. Even a small amount of blood can change the color of urine dramatically, so the intensity of the color doesn’t reliably tell you how much blood is present. Invisible (microscopic) hematuria shows up only when a lab examines your urine sample under magnification. The standard threshold is more than 3 red blood cells per high-power field on a single properly collected sample, according to guidelines from the American Urological Association.
The distinction matters because the likelihood of a serious underlying cause differs between the two. Visible blood in urine carries a higher probability of being linked to bladder cancer (about 17% of cases in large reviews) compared to microscopic hematuria (roughly 3.3%). That doesn’t mean microscopic blood is harmless, but it does help explain why doctors approach the workup differently depending on what type you have.
The Most Common Causes
Urinary tract infections are probably the most frequent culprit, especially in women. Bacteria irritate the lining of the bladder or urethra, which can cause bleeding along with burning, urgency, and frequent urination. A simple urine culture confirms the diagnosis, and antibiotics typically clear it up.
Kidney stones are another leading cause. As a stone moves through the urinary tract, it scrapes the delicate tissue lining the ureter or bladder, producing blood that may be visible or microscopic. The hallmark symptom is intense, wave-like pain in the back or side, often radiating toward the groin.
In men over 50, an enlarged prostate frequently causes blood in the urine. The prostate surrounds the urethra, and when it grows, it can compress blood vessels and cause bleeding alongside difficulty urinating or a persistent urge to go. Prostate infections (prostatitis) produce similar symptoms.
A kidney condition called glomerulonephritis, where the tiny filtering units inside the kidneys become inflamed, is a common source of microscopic hematuria. It can develop on its own or as part of a systemic condition like diabetes. When significant protein also appears in the urine alongside the blood, it points toward this kind of kidney-based cause rather than a problem lower in the urinary tract.
When Cancer Is the Cause
Cancer is what most people worry about when they see blood in their urine, and it’s worth understanding the actual numbers. A large systematic review in European Urology found that among people with visible hematuria, about 17% had bladder cancer and 2% had kidney cancer. For those with only microscopic hematuria, the rates dropped to 3.3% for bladder cancer and under 1% for kidney cancer. Upper urinary tract cancers were rarer still, under 1% for visible and roughly 0.2% for microscopic blood.
The risk rises with age, a history of smoking, and exposure to certain industrial chemicals. Bladder cancer is the most common urinary tract malignancy, and painless visible hematuria in someone over 50 is the classic presentation that prompts an urgent evaluation. Finding it early makes a significant difference in outcomes, which is why any episode of unexplained visible blood in urine warrants investigation rather than a wait-and-see approach.
Causes That Aren’t Actually Blood
Not everything that turns your urine red is blood. Beets are a well-known offender. They contain a pigment called betanin that some people can’t fully break down, resulting in pink or red urine within a day or two of eating them. Dragon fruit, blackberries, and rhubarb can do the same thing. Heavily dyed red foods can also change urine color temporarily.
If you’ve eaten any of these within the past 48 hours, that’s likely the explanation. If you haven’t, or if the discoloration persists beyond a couple of days, it’s worth getting a urine test to check for actual blood cells.
Exercise-Related Bleeding
Strenuous exercise, particularly long-distance running, can cause blood to appear in urine. The leading theory is that the posterior wall of the bladder repeatedly slams against its base during impact activities, especially when the bladder is nearly empty. Some evidence also suggests the prostate can sustain minor exercise-related injury that contributes to bleeding in men.
The reassuring part: exercise-induced hematuria is typically painless and resolves on its own within 48 to 72 hours, often clearing within just a few voids after stopping the activity. If it doesn’t resolve within that window, or if it happens repeatedly, further testing is reasonable to rule out an underlying issue that exercise is simply unmasking.
Medications That Can Cause It
Blood thinners are a common contributor. Warfarin, apixaban, and dabigatran can all make hematuria more noticeable, though it’s important to understand that these drugs usually amplify bleeding from a pre-existing source rather than creating a problem from scratch. Finding blood in your urine while on a blood thinner still warrants investigation of the underlying cause.
Other medications linked to hematuria include certain antibiotics (penicillin-type drugs, aminoglycosides), some antidepressants, diuretics, pain relievers, oral contraceptives, and anticonvulsants. If you notice a change after starting a new medication, mention it to your prescriber, but don’t assume the drug is the sole explanation without testing.
How It Gets Diagnosed
The first step is usually a urine dipstick test, which detects blood based on a chemical reaction. It’s sensitive (catches about 95% of cases) but not perfectly specific (about 75%), meaning it occasionally flags blood that isn’t actually there. That’s why a positive dipstick is followed by microscopic examination of the urine sediment to confirm real red blood cells are present and count how many.
From there, the workup depends on the type of hematuria and your risk factors. For visible hematuria, the standard evaluation includes three components: a direct look inside the bladder with a small camera (cystoscopy), imaging of the upper urinary tract with a CT or MRI scan, and a urine cytology test that checks for abnormal cells. Blood tests measuring kidney function, blood cell counts, and clotting ability often round out the picture. In men, a PSA test may be included depending on age and risk factors.
For microscopic hematuria without other symptoms, the approach is more measured. Your doctor will consider your age, smoking history, and other risk factors to decide whether imaging and cystoscopy are needed right away or whether monitoring with repeat urine tests is appropriate first.
What Different Colors Can Tell You
Pink or light red urine usually indicates a small amount of fresh blood, often from the bladder or urethra. Dark red or cola-colored urine suggests the blood has been sitting longer or originates higher in the urinary tract, such as the kidneys. Bright red with visible clots points to more active bleeding and typically prompts a more urgent evaluation. Keep in mind that even a single milliliter of blood can visibly discolor an entire toilet bowl, so the appearance can be more alarming than the actual volume of blood lost.
If your urine is red but a dipstick comes back negative for blood, the cause is likely dietary (beets, berries) or medication-related rather than a true bleed.