More than 2 white blood cells per high-power field on a microscopic urine exam is generally considered abnormal, and 5 or more per high-power field is the threshold most clinicians use to flag a significant finding. If your urine test came back showing elevated leukocytes (white blood cells), it usually means your urinary tract is inflamed, most often from an infection.
What the Numbers Mean
When a lab analyzes your urine under a microscope, they count white blood cells in a small viewing area called a high-power field (hpf). A normal result is 0 to 5 white blood cells per hpf. Two or more per field in a clean, uncontaminated sample can be abnormal, and counts well above 5 per hpf point strongly toward active inflammation somewhere in the urinary tract.
Most people first learn about elevated leukocytes through a dipstick test rather than a microscope. The dipstick detects an enzyme released by white blood cells called leukocyte esterase. Results show up as negative, trace, small, moderate, or large. “Trace” can sometimes be insignificant, but “moderate” or “large” typically prompts further testing. In symptomatic older adults, the dipstick picks up about 92% of true infections, but it also flags many people who don’t actually have one, with a specificity of only about 39%. That means a positive dipstick is a starting point, not a diagnosis.
Why White Blood Cells End Up in Urine
White blood cells don’t belong in urine in large numbers. When tissue anywhere along the urinary tract becomes inflamed, blood vessels in the area dilate and become more permeable. White blood cells squeeze through the vessel walls and migrate into surrounding tissue and eventually into the urine. This process, called diapedesis, is the body’s standard response to infection or injury. The more severe the inflammation, the more white blood cells appear.
Urinary Tract Infections
The most common reason for high leukocytes in urine is a UTI. Bacteria enter the urethra, multiply in the bladder, and trigger an immune response that floods the area with white blood cells. Typical symptoms include pain or burning during urination, needing to go more often than usual, cloudy or foul-smelling urine, and pain in the lower belly, back, or side. Some people also experience nausea and vomiting, especially if the infection has spread to the kidneys.
If your dipstick also shows nitrites (a byproduct of certain bacteria), that’s a stronger signal that bacteria are present. Home UTI test kits check for both leukocytes and nitrites for this reason. However, not all bacteria produce nitrites, so a negative nitrite result doesn’t rule out infection if leukocytes are elevated and you have symptoms.
Non-Infectious Causes
High leukocytes without an active bacterial infection, sometimes called sterile pyuria, has several possible explanations. Kidney stones can scrape and irritate the lining of the urinary tract, triggering white blood cell migration without any bacteria involved. Symptoms of kidney stones include sharp pain in the side, back, or groin, blood in the urine (which may look pink, red, or brown), and an urgent need to urinate.
Inflammation of the bladder wall (interstitial cystitis) or kidney tissue (interstitial nephritis) can also push leukocyte counts up. These conditions cause frequent urination, an increased urge to go, blood in the urine, and sometimes fever or nausea. Interstitial nephritis may also cause swelling in the feet. Certain medications, autoimmune conditions, and urinary catheterization are additional triggers.
In rare cases, persistently elevated white blood cells in urine can be associated with cancers of the urinary tract or blood cancers like leukemia. These typically come with other symptoms: unexplained weight loss, fatigue, night sweats, or fever that doesn’t resolve.
False Positives and Sample Contamination
Not every positive result reflects a real problem in your urinary tract. Contamination is one of the most common reasons for a misleading result, particularly in women. Vaginal secretions contain white blood cells, and if they mix with the urine sample during collection, the test can read as abnormally high. Heavy menstrual discharge and Trichomonas infections (a common vaginal parasite) are frequent culprits. Oxidizing agents and certain preservatives can also produce false positives on the dipstick.
This is why a “clean-catch” midstream sample matters. If your first result is positive and your doctor suspects contamination, you may be asked to provide a more carefully collected sample or move on to a urine culture, which identifies specific bacteria and rules out a false alarm.
When a Urine Culture Is Needed
A dipstick or microscopic exam tells you inflammation is present. A urine culture tells you whether bacteria are actually growing, which ones they are, and which treatments will work against them. Current European urology guidelines recommend a culture in several situations: when symptoms are unusual or don’t clearly point to a simple bladder infection, when symptoms don’t improve or come back within four weeks of treatment, when there’s concern about a kidney infection (pyelonephritis), when UTIs keep recurring, and for anyone at higher risk of drug-resistant bacteria. Pregnant women with elevated leukocytes should also have a culture done.
Leukocytes in Urine During Pregnancy
Pregnancy makes urinary tract infections both more common and more consequential. Hormonal changes relax the muscles of the ureters, slowing urine flow and giving bacteria more opportunity to take hold. The diagnostic threshold stays at 5 or more white blood cells per high-power field.
The stakes are higher because an untreated urinary infection during pregnancy can escalate to kidney damage, preterm labor, or preeclampsia. Even asymptomatic bacteria in the urine (no burning, no frequency) can progress to a serious infection in pregnant women, which is why routine urine screening is standard at prenatal visits.
Catheters and Leukocyte Readings
If you or a family member has a urinary catheter, elevated leukocytes are extremely common and don’t automatically mean infection. Catheters irritate the bladder lining, which draws white blood cells into the urine even without bacteria. Current guidelines are clear that pyuria alone should not be used to diagnose a catheter-associated UTI and should not trigger antibiotic treatment by itself. The absence of pyuria in someone with catheter-related symptoms, on the other hand, suggests the problem is something other than a UTI. If infection is suspected, a urine culture from a freshly placed catheter should be collected before starting any treatment.