Blood in your urine can come from anywhere along the urinary tract, from the kidneys down to the urethra. The most common causes are urinary tract infections, kidney or bladder stones, and an enlarged prostate in men. Less often, it signals kidney disease or a cancer in the urinary tract. Sometimes what looks like bloody urine turns out to be harmless discoloration from foods like beets or blackberries.
There are two types. Gross hematuria is blood you can see, turning urine pink, red, or cola-colored. Microscopic hematuria is invisible to the naked eye and only shows up on a lab test. Both warrant attention, though the causes overlap considerably.
Urinary Tract Infections
Bacterial infections in the bladder, kidneys, or urethra are one of the most frequent reasons for blood in urine, especially in women. When bacteria invade the lining of the urinary tract, they trigger inflammation that damages small blood vessels in the tissue. This lets red blood cells leak into the urine. You’ll usually have other symptoms alongside the blood: burning during urination, a constant urge to go, cloudy or strong-smelling urine, and sometimes pelvic pressure or lower back pain. A kidney infection can add fever, chills, and flank pain to the mix. Antibiotics typically clear the infection, and the bleeding stops once the inflammation settles.
Kidney and Bladder Stones
Minerals dissolved in urine can crystallize on the walls of the kidneys or bladder and, over time, harden into stones. These stones cause blood in the urine both by scraping the delicate lining of the urinary tract and by creating irritation as they move. Stones are often painless while they sit still. The intense pain people associate with kidney stones, a sharp, wave-like cramping in the back or side, happens when a stone blocks urine flow or travels down the narrow tube connecting the kidney to the bladder. Some people discover they have stones only because a routine urine test picks up microscopic blood, with no pain at all.
Enlarged Prostate
In men, the prostate gland surrounds the urethra just below the bladder. As men age, the prostate commonly enlarges, a condition called benign prostatic hyperplasia (BPH). The growth creates congested blood vessels in the prostate and at the bladder neck that are fragile and prone to bleeding. If you have BPH, you may also notice a weak urine stream, difficulty starting urination, frequent nighttime trips to the bathroom, or a feeling that your bladder doesn’t fully empty. Blood from an enlarged prostate is usually not dangerous on its own, but it always needs evaluation because the same symptoms can overlap with more serious conditions like prostate or bladder cancer.
Kidney Filtering Problems
Your kidneys filter blood through millions of tiny structures called glomeruli, each packed with microscopic blood vessels. Normally these filters let water, minerals, and waste pass through while keeping red blood cells and large proteins in the bloodstream. When the filters become inflamed or damaged, red blood cells slip through into the urine.
One of the more common forms of this is IgA nephropathy. In this condition, an immune system protein that normally fights infections builds up in the kidney filters, causing inflammation that worsens over time. The hallmark sign is cola- or tea-colored urine, often appearing during or shortly after a cold or other respiratory infection. Some people also develop foamy urine from protein leaking through the damaged filters, along with swelling in the feet, eyelids, or abdomen. Other forms of kidney inflammation can follow autoimmune diseases, certain infections, or run in families. These conditions need monitoring because they can gradually reduce kidney function if left untreated.
Bladder and Kidney Cancer
Painless blood in the urine is the most common symptom of bladder cancer and the most common symptom of kidney cancer. That word “painless” is key: unlike infections or stones, cancer-related bleeding often shows up without any burning, cramping, or other warning signs. The blood may appear once, disappear for weeks, then return. This intermittent pattern sometimes leads people to dismiss it.
Bladder cancer is more common in people over 55, smokers, and those exposed to certain industrial chemicals. Kidney cancer shares some of the same risk factors. The earlier either cancer is caught, the more treatment options are available and the better the outcomes. Visible blood in the urine that you can’t explain with an obvious cause like a known infection deserves prompt evaluation, even if it goes away on its own.
Intense Exercise
Strenuous physical activity, particularly long-distance running, cycling, or high-intensity training, can temporarily cause blood in the urine. Several mechanisms are at play: reduced blood flow to the kidneys during prolonged exertion, increased body temperature, dehydration concentrating the urine, exercise-related acid buildup, and direct trauma to the bladder wall from repetitive impact (common in runners whose partially empty bladder bounces with each stride). Contact sports can also cause it through a direct blow to the flank or lower back that injures the kidney. Exercise-induced hematuria generally resolves within 24 to 72 hours. If it persists beyond that, or if it happens repeatedly, other causes need to be ruled out.
Blood Thinners and Medications
If you take blood-thinning medications (anticoagulants), you might assume they’re the reason blood appears in your urine. That’s sometimes partly true, since these drugs make bleeding from any source last longer or become more noticeable. But research shows that roughly 30% of patients who develop blood in the urine while on blood thinners, even when their medication levels are in the normal therapeutic range, turn out to have a significant underlying urinary tract condition causing the bleeding. Blood thinners may simply unmask a problem that was already there. For this reason, hematuria while on anticoagulants still warrants a full evaluation rather than being chalked up to the medication alone.
Foods That Mimic Blood in Urine
Before assuming the worst, consider what you’ve eaten in the past 48 hours. Beets are the most well-known culprit, producing a pink or reddish tinge to urine that’s sometimes called “beeturia.” Dragon fruit, blackberries, rhubarb, and heavily red-dyed foods can do the same. Certain medications also change urine color to orange, red, or brown. The simple way to tell the difference: if the discoloration clears within a day or two after you stop eating the suspect food and a urine test shows no red blood cells, it’s not hematuria.
How Blood in Urine Is Evaluated
The first step is a urinalysis, a lab test that examines a urine sample under a microscope. Microscopic hematuria is defined as more than 3 red blood cells per high-power field on a single properly collected sample. If blood is confirmed, your doctor categorizes your risk level based on factors like age, smoking history, how much blood is present, and whether you have other symptoms.
For low-risk patients, a repeat urinalysis within six months is often sufficient. Intermediate-risk patients typically undergo an ultrasound of the kidneys and bladder, and may be recommended a cystoscopy, an office procedure where a thin, flexible camera is passed through the urethra to visually inspect the bladder lining. No sedation is usually required. High-risk patients get both cystoscopy and a CT urogram, a multi-phase scan that images the kidneys, ureters, and bladder in detail. The first phase detects stones without contrast dye, the second identifies kidney masses, and a delayed phase taken about 15 minutes later shows the entire drainage system after contrast has been filtered through the kidneys.
This risk-based approach, outlined in the 2025 American Urological Association guidelines, aims to avoid unnecessary procedures for people at low risk while ensuring that potentially serious causes aren’t missed in those at higher risk. The goal of every evaluation is the same: find the source of bleeding, or confirm that no dangerous cause exists.