Gross hematuria, visible blood in your urine, can be caused by urinary tract infections, kidney stones, an enlarged prostate, kidney disease, cancer, intense exercise, or certain medications. It takes only a small amount of blood to turn urine pink, red, or cola-colored, so the appearance can be alarming even when the underlying cause is minor.
Urinary Tract Infections
Infections are one of the most common reasons for blood in the urine. When bacteria invade the lining of the bladder or urethra, they trigger inflammation that damages the tissue surface, allowing blood to seep into the urine. Kidney infections can do the same thing higher up in the urinary tract, and they tend to produce more dramatic bleeding along with fever and flank pain. Women develop UTIs far more often than men due to a shorter urethra, making infections a particularly frequent explanation for gross hematuria in women.
Kidney Stones
Stones that form in the kidneys or ureters can scrape and irritate the lining of the urinary tract as they move. This physical trauma causes bleeding that ranges from faintly pink urine to visibly red. You’ll usually know a stone is involved because it causes intense, cramping pain in the side or lower back that comes in waves. Small stones may pass on their own within days, while larger ones sometimes require procedures to break them apart.
Enlarged Prostate
In men, a common cause of gross hematuria is benign prostatic hyperplasia (BPH), the gradual enlargement of the prostate gland that happens with age. As the prostate grows, the blood vessels in the prostate and at the bladder neck become congested and fragile. These engorged vessels can rupture and bleed into the urine. However, blood in the urine in a man with a known enlarged prostate still warrants evaluation, because hematuria can also signal a separate problem like a stone or a malignancy that happens to coexist with BPH.
Kidney Filtering Problems
Sometimes blood enters the urine not because of a structural injury but because the kidney’s filtering units aren’t working properly. In a condition called IgA nephropathy, the immune system deposits proteins in the kidney’s filters, causing them to leak red blood cells. This is most common in children and young adults, and roughly 80% of flare-ups happen alongside an upper respiratory infection, such as a sore throat. Visible blood typically appears within the first 48 to 72 hours of getting sick, lasts fewer than three days, and may come with a dull ache in the side from kidney swelling. Most of these patients, especially children, go into remission.
In children specifically, a condition called post-streptococcal glomerulonephritis can cause dark, reddish-brown urine a week or two after a strep throat or skin infection. It’s most common in preschool and early school-age kids. Over 90% of children recover fully, though adults who develop it are more likely to have lasting kidney effects.
Cancer of the Urinary Tract
Gross hematuria is sometimes the first sign of bladder, kidney, or (in men) prostate cancer. In a large study of more than 3,500 patients referred for evaluation of blood in their urine, about 13% of those with gross hematuria turned out to have a urinary tract cancer. Bladder cancer specifically was found in nearly 11% of high-risk patients with gross hematuria. These numbers are high enough that visible blood in the urine almost always prompts a thorough workup, especially in adults over 40 or those with risk factors like smoking.
The bleeding from urinary tract cancers is typically painless, which is part of what makes it easy to dismiss. Painless gross hematuria in an older adult is treated as a red flag until imaging and a scope exam of the bladder can rule out malignancy.
Medications
Blood thinners can unmask or worsen bleeding from a source in the urinary tract that might otherwise go unnoticed. But some medications directly damage the bladder lining, causing a condition called hemorrhagic cystitis. The most well-known culprit is cyclophosphamide, a chemotherapy drug. When the liver breaks it down, it produces a byproduct called acrolein that is excreted through the urine and is directly toxic to the bladder wall. Patients on this drug are typically given protective agents to reduce the risk, but breakthrough bleeding still occurs.
Less commonly, certain other medications have been linked to bladder irritation and bleeding, though reports are limited. In nearly all documented cases, the hematuria resolved after the medication was stopped.
Intense Exercise
Distance runners and endurance athletes sometimes notice blood in their urine after a hard workout. The mechanism behind “runner’s bladder” appears to be repeated impact of the bladder wall against its base during sustained running, essentially a bruising effect on the inside of the bladder. Whether the blood originates from the bladder or the kidneys, it typically clears within 24 to 48 hours after stopping the activity. If it doesn’t resolve in that window, or if it happens repeatedly, it warrants a closer look to rule out other causes.
Trauma
A direct blow to the kidney or bladder, whether from a car accident, a fall, or a contact sport, can cause blood to appear in the urine. The severity depends on the force involved. Minor kidney bruising may produce temporary pink-tinged urine, while a more serious injury to the kidney or a bladder rupture typically causes heavy bleeding and requires urgent care.
When Gross Hematuria Is an Emergency
Most causes of gross hematuria are not immediately dangerous, but there are situations that require urgent attention. Large blood clots can block the flow of urine out of the bladder, causing painful retention. Heavy, sustained bleeding can, in rare cases, lead to low blood pressure and shock. If you notice clots in your urine, can’t urinate despite feeling the urge, or feel lightheaded alongside visible blood in the urine, that’s a situation for emergency care rather than a scheduled appointment.
Even when gross hematuria seems to resolve on its own, a single episode in an adult typically prompts a full evaluation. The fact that the bleeding stopped doesn’t mean the cause has gone away, and conditions like bladder cancer can bleed intermittently for months before being caught.