White blood cells in your urine typically signal inflammation somewhere in your urinary tract. The most common cause is a urinary tract infection (UTI), but infections aren’t the only explanation. Kidney stones, certain medications, sexually transmitted infections, and inflammatory conditions can all trigger your immune system to send white blood cells into the urinary tract, where they show up on a urine test.
How White Blood Cells End Up in Urine
Your body sends white blood cells wherever it detects a threat, whether that’s bacteria, physical irritation, or inflammation. When the threat involves your kidneys, bladder, or the tubes connecting them, those white blood cells pass into your urine. A normal urine sample contains very few white blood cells. When the count rises above about 5 cells per high-power field under a microscope, it’s considered elevated, a condition called pyuria.
Most urine tests start with a dipstick, a chemical strip that detects an enzyme released by white blood cells. If that enzyme shows up, the sample may be examined under a microscope for a more precise count. Dipstick tests are good at ruling out problems (they correctly identify normal samples about 95% of the time), but they can also flag false positives, especially during pregnancy, when shed cells from the vaginal lining can be mistaken for white blood cells.
UTIs: The Most Common Cause
A urinary tract infection is the first thing most providers consider when white blood cells appear in urine. Bacteria enter the urethra, multiply in the bladder, and trigger an immune response. You’ll usually notice burning during urination, a frequent urge to go, cloudy or strong-smelling urine, or pelvic pressure.
If your urine also tests positive for nitrites, the likelihood of a bacterial UTI goes up. Certain bacteria convert naturally occurring nitrates in urine into nitrites, so finding both nitrites and white blood cells together is a strong signal. That said, not all bacteria produce nitrites, so a negative nitrite result doesn’t rule out infection.
When Bacteria Don’t Show Up
Sometimes a urine culture comes back negative even though white blood cells are clearly elevated. This is called sterile pyuria, and it has a surprisingly long list of causes. The key point: “sterile” doesn’t always mean there’s no infection. Several organisms simply don’t grow on standard lab cultures.
Sexually transmitted infections caused by chlamydia, gonorrhea, or trichomonas are a common culprit, particularly in younger adults. These organisms cause inflammation in the urethra or genital tract, sending white blood cells into the urine, but they require specialized testing to detect. Urinary tuberculosis is another infection that won’t appear on a routine culture. It accounts for roughly 30% of tuberculosis cases outside the lungs and can be detected in up to 46% of affected men through urine testing.
Viral and fungal infections of the urinary tract can also produce white blood cells without a positive bacterial culture. Even infections near the urinary tract, like appendicitis, pelvic inflammatory disease, or diverticulitis, can cause inflammation that spills white blood cells into urine.
Non-Infectious Causes
Not every case involves an infection at all. Several other conditions can explain elevated white blood cells in urine:
- Kidney stones: Stones irritate the lining of the urinary tract, triggering an inflammatory response even without bacteria present.
- Interstitial cystitis: This chronic bladder pain condition causes persistent inflammation of the bladder wall.
- Autoimmune diseases: Lupus, sarcoidosis, and other systemic inflammatory conditions can cause the kidneys to release white blood cells into urine as part of widespread inflammation.
- Medications: NSAIDs (like ibuprofen), certain antibiotics, proton pump inhibitors (heartburn medications), and diuretics (water pills) can irritate the kidney’s filtering tissue, a reaction called interstitial nephritis. This is one of the more overlooked causes.
- Pregnancy: White blood cells in urine are common during pregnancy and don’t always indicate a problem, though providers monitor for UTIs closely because untreated infections carry higher risks during pregnancy.
- Recent urological procedures: Catheter use, surgery, or even retained devices like stents can cause local inflammation.
What Your Results Tell You About Location
The type of white blood cells found can hint at where the problem is. When white blood cells clump together into tube-shaped structures called casts, it points to the kidneys specifically, often a kidney infection or inflammation of the kidney’s filtering tissue. Simple scattered white blood cells are less specific and could indicate a problem anywhere from the kidneys down to the urethra.
Your provider pieces this together with your symptoms. Flank pain and fever alongside white blood cell casts suggest a kidney infection. Burning and urgency with white blood cells but no casts point more toward a bladder infection. No symptoms at all, combined with a negative culture, opens the door to the longer list of possibilities above.
When There Are No Symptoms
Finding white blood cells in urine during a routine test, with no symptoms and no bacteria on culture, is a common scenario. In many cases, it doesn’t require treatment. Pregnancy is one important exception, where even symptom-free bacteria in the urine are typically treated because of the risk of complications.
Persistent sterile pyuria, white blood cells that keep showing up across multiple tests without a clear bacterial cause, does warrant further investigation. Providers will typically consider whether a sexually transmitted infection was missed, whether medications could be responsible, or whether an imaging study is needed to look for stones, structural problems, or, rarely, tumors. In areas where tuberculosis is more common, urine testing for TB may be part of that workup.
What to Expect After an Abnormal Result
If your urine test shows elevated white blood cells, the next steps depend on the full picture. A positive culture with symptoms usually means a straightforward course of antibiotics. A positive culture without symptoms in a non-pregnant adult often means no treatment is needed.
When the culture is negative but white blood cells are elevated, your provider may order STI testing, repeat the urinalysis to confirm the finding, or request imaging of the kidneys and bladder. If you’ve recently started a new medication, especially an NSAID, heartburn drug, or diuretic, mention it, since drug-related kidney irritation is both common and easily reversible once the medication is stopped.
A single elevated reading on one test is rarely cause for alarm on its own. The pattern across repeated tests, combined with your symptoms and medical history, is what guides the diagnosis.