Blood in the urine, called hematuria, is surprisingly common in women. In a large study of over 2.7 million women, about 20% had blood detected on a urine test at some point. The causes range from urinary tract infections, which are by far the most frequent explanation, to rarer conditions like bladder cancer. Most of the time the cause is treatable and not dangerous, but visible blood or blood that keeps showing up on tests deserves a workup.
Visible vs. Hidden Blood
Blood in urine falls into two categories. Visible (gross) hematuria turns your urine pink, red, or brownish. It only takes a small amount of blood to change the color noticeably. Microscopic hematuria, on the other hand, can only be picked up by a lab test. The standard threshold is three or more red blood cells per high-power field on a microscope slide, though there is no truly “safe” lower number.
Both types can point to the same underlying causes. The difference matters mainly for risk: a history of visible blood in the previous six months is one of the strongest predictors of a serious underlying problem, carrying roughly six times the odds of a urologic cancer compared to microscopic blood alone.
Urinary Tract Infections
UTIs are the single most common reason women see blood in their urine. Bacteria enter the urethra and multiply in the bladder, inflaming the lining enough to cause bleeding. Along with pink or red urine, a UTI typically brings a persistent, urgent need to pee, burning during urination, and strong-smelling urine. Women are more prone to UTIs than men because of a shorter urethra, and most cases clear with a course of antibiotics.
Kidney Stones
Kidney stones are another frequent culprit. About 85% of people with a stone will have at least microscopic blood in their urine. The hallmark symptom is sudden, severe pain in the flank that often radiates to the lower abdomen and groin or labia. The pain tends to come in waves as the ureter spasms around the stone. Some stones pass on their own over days to weeks; larger ones may need a procedure to break them up or remove them.
Causes Specific to Women
A few causes are unique to female anatomy. Endometrial tissue, the lining that normally grows inside the uterus, can sometimes implant on the bladder wall. This bladder endometriosis affects only about 1 to 2% of women with endometriosis overall, but when it does occur, the bladder is involved roughly 84% of the time. The classic clue is cyclical hematuria: blood in the urine that appears around the time of your period, often alongside pelvic pressure and urgency. That said, only about 20% of women with bladder endometriosis actually experience this textbook pattern, so it can be missed.
Vaginal bleeding from menstruation, cervical irritation, or postmenopausal changes can also contaminate a urine sample and mimic hematuria. If a urine test comes back positive for blood, your provider may ask you to repeat it at a different point in your cycle or collect the sample more carefully to rule out contamination.
During Pregnancy
Dipstick hematuria is very common during pregnancy. Research tracking pregnancy outcomes found that women with and without blood on a urine dip had similar rates of preeclampsia, gestational hypertension, and small-for-gestational-age babies. In other words, the blood itself rarely signals a problem that will affect the pregnancy. It is often related to the increased UTI risk that comes with pregnancy or to normal changes in kidney blood flow. Postpartum follow-up is still a good idea, because persistent hematuria after delivery can occasionally point to mild underlying kidney inflammation.
Exercise-Related Bleeding
Intense physical activity, particularly long-distance running, can cause blood in the urine without any disease being present. Two mechanisms are at play: reduced blood flow to the kidneys during hard effort, and repeated impact of the bladder wall against itself when the bladder is relatively empty during a run. The reassuring part is that exercise-induced hematuria almost always resolves within 24 to 48 hours of rest. If it does not clear by then, something else is likely going on.
When It Could Be Cancer
This is usually the fear behind the search, and the numbers are worth knowing. In a study of over 3,500 women evaluated for microscopic hematuria, the overall rate of urologic cancer was 1.3%. Among women under 40 with microscopic blood, the rate of any urinary malignancy dropped to just 0.02%. For women over 40, it rose to about 0.4%. In low-risk women, meaning never-smokers under 50 without visible blood and with relatively few red blood cells on the slide, the risk is 0.5% or less.
The three factors most strongly linked to cancer in women with hematuria are age over 60, a history of smoking, and a history of visible (gross) hematuria. Smoking roughly tripled the odds, and being over 60 tripled them as well. If none of those risk factors apply to you, cancer is a statistically unlikely explanation, though it is never fully ruled out without appropriate testing.
Red Flags That Need Urgent Attention
Most hematuria can be evaluated at a routine appointment, but certain combinations of symptoms warrant same-day or emergency care:
- Passing blood clots that make it difficult to urinate or that block urine flow entirely
- Lightheadedness, rapid heartbeat, or feeling faint, which can signal significant blood loss
- Fever with chills and flank pain, suggesting an infection has spread to the kidneys
- Sudden inability to urinate despite feeling the urge
- Hematuria after an injury to the abdomen, pelvis, or back
What to Expect During Evaluation
For a first episode of microscopic hematuria found on a routine test, your provider will typically repeat the urinalysis to confirm the result, especially if you were menstruating or had recently exercised. If the blood persists, the next steps usually include imaging of the kidneys and bladder (often an ultrasound or CT scan) and, for women over 35 or those with risk factors, a cystoscopy, which is a thin camera passed through the urethra to inspect the bladder lining directly. A urine culture checks for infection, and sometimes a urine sample is sent for cytology to look for abnormal cells.
For younger women with no risk factors and a single episode of microscopic hematuria, monitoring with repeat urine tests over the following year is sometimes all that is needed. The goal is to catch any persistent or worsening bleeding early while avoiding unnecessary procedures in women whose risk of serious disease is very low.