Blood in urine, called hematuria, is usually a sign that something is irritating or damaging your urinary tract. It can range from a minor issue like a urinary tract infection to something more serious like a kidney stone or, in roughly 11% of cases involving visible blood, a tumor. The cause varies significantly by age, but any instance of blood in your urine warrants attention and follow-up.
Sometimes the blood is obvious, turning your urine pink, red, or cola-colored. Other times it’s invisible to the naked eye and only shows up on a lab test. Both matter, and both deserve investigation, but visible blood tends to carry a higher likelihood of a significant underlying cause.
What Visible Blood Looks Like
Visible blood in urine (gross hematuria) can appear as anything from a faint pink tinge to a deep red or brown. Even a small amount of blood can dramatically change the color. You might also notice small clots. The color alone doesn’t reliably tell you where the bleeding is coming from or how serious it is.
Microscopic hematuria, by contrast, is defined as three or more red blood cells per high-power field under a microscope. You’d never know it was there without a urinalysis. It’s frequently discovered during routine checkups and, while often benign, still needs to be evaluated.
The Most Common Causes
Several conditions can cause blood in urine, and some are far more common than others.
Urinary tract infections. Bacteria enter the urethra and multiply in the bladder, causing inflammation that damages small blood vessels in the lining. Along with blood in urine, you’ll typically notice burning during urination, urgency, and sometimes a strong odor. UTIs are less common in men than women but do occur, particularly in older men.
Kidney or bladder stones. Minerals in urine crystallize over time into hard deposits. These stones can scrape the lining of the urinary tract as they move, causing bleeding that’s sometimes painless and sometimes agonizing. A stone passing through the ureter (the tube connecting your kidney to your bladder) often causes sharp, wave-like pain in the side or lower back.
Enlarged prostate. Benign prostatic hyperplasia (BPH) is extremely common in men over 50. As the prostate grows, it develops an increasingly rich blood supply. Those enlarged blood vessels near the surface of the gland can bleed into the urinary tract. BPH-related hematuria can be a one-time event or something that recurs.
Prostate or urinary tract infections. Prostatitis, an inflammation of the prostate caused by infection or other factors, can produce blood in urine along with pelvic pain, difficulty urinating, and sometimes fever.
Injury. A blow to the kidney from contact sports, a car accident, or a fall can cause bleeding. Even without dramatic trauma, certain activities put enough stress on the urinary tract to produce blood.
Exercise-Induced Hematuria
Blood in urine after intense exercise is common enough to have its own name: “runner’s bladder.” About 20 to 25% of runners experience some form of hematuria after running, though visible blood is rarer, affecting around 2% of marathon runners. Research using cystoscopy (a camera inserted into the bladder) found that in 75% of cases, the bleeding came from bruise-like contusions on the back wall of the bladder. The repeated impact of running causes the bladder walls to slap against each other, particularly when the bladder is empty.
The blood typically clears within a day or two without treatment. Half of the patients studied experienced it again after resuming running. Running with a partially full bladder and staying well-hydrated may help prevent it. Still, exercise-induced hematuria is a diagnosis of exclusion. If blood shows up after a workout, it’s worth getting checked to rule out other causes before assuming it’s benign.
When Cancer Is the Concern
This is the fear most people have when they search this topic, so here are the numbers. In a large population-based study, 11% of patients who presented with visible blood in their urine were eventually diagnosed with a malignant tumor. The most common was bladder cancer, found in 9% of those patients. Kidney cancer accounted for about 1.3%, and cancer of the upper urinary tract about 0.8%.
Certain factors raise the risk. Age is the biggest one: the older you are, the more likely hematuria is to signal cancer. A smoking history more than doubles the odds of bladder cancer in this setting. Being male also independently increases risk. This doesn’t mean blood in your urine is likely cancer, but it does mean that visible hematuria in a man over 50 who smokes should be evaluated promptly.
Kidney Filtering Problems
Sometimes blood in urine originates from the kidneys themselves, not from the bladder or prostate. Glomerulonephritis is a condition where the tiny filters in your kidneys become inflamed, usually due to an immune system response. This damage lets blood cells and protein leak through into your urine.
A clue that bleeding is coming from the kidneys rather than the lower urinary tract is the presence of protein in the urine alongside blood. The urine may look brown or tea-colored rather than bright red. Your doctor can examine the shape of red blood cells under a microscope to help determine whether they passed through damaged kidney filters (which distorts their shape) or entered the urine from somewhere lower in the tract.
It Might Not Be Blood at All
Before assuming the worst, consider what you’ve eaten or taken recently. Beets, blackberries, and rhubarb can all turn urine red or pink. So can several medications: rifampin (a tuberculosis drug) turns urine reddish-orange, phenazopyridine (a common bladder pain reliever) does the same, and laxatives containing senna can cause a similar color shift. A simple urinalysis will confirm whether actual blood cells are present or whether the color has a harmless explanation.
What Happens During Evaluation
The first step is a urinalysis, which checks for blood cells, protein, signs of infection, and other abnormalities. If blood is confirmed, the evaluation typically follows a risk-based approach. Your doctor will consider your age, smoking history, the amount of blood, and whether you have any other symptoms.
For many patients, the next steps include imaging of the urinary tract (often a CT scan with contrast that highlights the kidneys, ureters, and bladder) and cystoscopy, where a thin camera is passed through the urethra to directly examine the bladder lining. These two tests together can identify or rule out the most concerning causes, including stones, structural abnormalities, and tumors. The American Urological Association updated its guidelines in 2025 with a revised risk stratification system that helps determine how urgently and how extensively a person needs to be evaluated.
Symptoms That Need Immediate Attention
Most hematuria can be evaluated over the course of days to weeks, not hours. But certain situations call for urgent care. If you’re passing large clots and find yourself unable to urinate, that’s clot retention, and it requires immediate intervention. Other red flags include lightheadedness or rapid heart rate (signs of significant blood loss), fever with chills (suggesting an infection spreading beyond the urinary tract), and severe flank pain with blood in urine (which could indicate a kidney obstruction or injury).
A single episode of pink-tinged urine that clears on its own still deserves a doctor visit, just not necessarily a trip to the emergency room. Persistent or recurrent visible blood, on the other hand, should move up your priority list, especially if you’re over 40 or have a history of smoking.