Leukocytes in urine are white blood cells that have migrated into the urinary tract, usually signaling that your immune system is fighting an infection or responding to inflammation. A normal urine sample contains very few: 0 to 5 white blood cells per high-power field under a microscope, with men typically having fewer than 2 and women fewer than 5. When levels rise above that range, something is triggering your body’s defenses.
Why White Blood Cells Show Up in Urine
White blood cells are part of your immune system. When bacteria enter the urinary tract through the urethra, or when tissue in the kidneys or bladder becomes inflamed, your body sends white blood cells to the area to destroy the threat. Some of those cells end up in your urine, where they can be detected on a routine test.
The medical term for elevated white blood cells in urine is pyuria. It’s not a diagnosis on its own. It’s a sign that points toward an underlying cause, and the most common one by far is a urinary tract infection.
How Leukocytes Are Detected
Most of the time, leukocytes are first picked up on a simple dipstick test. A small strip with a color-sensitive pad is dipped into your urine sample. The pad reacts to an enzyme released by white blood cells, and the color change tells your provider whether leukocytes are present and roughly how many.
If the dipstick comes back positive, the next step is often urine microscopy, where a lab technician examines the sediment under a microscope to count cells directly and look for bacteria, crystals, or other abnormalities. A urine culture may also be ordered, especially if there’s concern about a kidney infection, if initial antibiotic treatment hasn’t worked, or during pregnancy. The culture identifies the specific bacteria involved and helps guide treatment.
Common Causes
Urinary tract infections are the leading cause. Bacteria entering through the urethra trigger an immune response, and you’ll typically notice burning during urination, a frequent urge to go, or pelvic pressure alongside the lab finding.
Kidney stones and other urinary obstructions are another frequent cause. When a stone blocks the normal flow of urine, the stagnant urine creates a breeding ground for bacteria, which in turn draws white blood cells to the area.
Sexually transmitted infections, particularly chlamydia in younger, sexually active people, can also elevate leukocyte counts. Gonorrhea, syphilis, and HPV have all been linked to the finding as well. In older adults, prostatitis or inflammation of the bladder lining may be responsible.
Less commonly, leukocytes in urine can reflect systemic conditions like lupus, sarcoidosis, or diabetes, or can appear after pelvic radiation therapy, urinary tract procedures, or with indwelling catheters.
When Bacteria Aren’t Found
Sometimes the dipstick or microscopy shows white blood cells, but a urine culture comes back negative for bacteria. This is called sterile pyuria, generally defined as more than 5 to 8 white blood cells per high-power field with no bacterial growth. It’s more common than many people expect and has a long list of potential explanations.
One of the most frequent is a recently treated UTI. Even a single dose of antibiotics can clear the bacteria while the inflammatory response lingers for up to two weeks. Viral infections, including adenovirus, can also cause it. In people with persistent sterile pyuria, providers consider less obvious infections like renal tuberculosis.
Non-infectious causes include interstitial cystitis (a chronic bladder pain condition), kidney stones, polycystic kidney disease, and nearby pelvic inflammation from something like appendicitis irritating the bladder or ureter. Pregnancy and post-menopausal hormonal changes can produce it as well.
Medications are an underrecognized cause. Long-term use of common over-the-counter pain relievers like ibuprofen, naproxen, or aspirin can trigger inflammation in the kidney’s filtering tubes. Penicillin-based antibiotics, diuretics, and acid-reducing stomach medications have also been implicated.
Leukocytes in Urine During Pregnancy
Pregnant women are routinely screened for leukocytes because UTIs during pregnancy carry higher risks, including preterm labor and kidney infection. Several pregnancy-specific factors raise the likelihood of a positive result: hormonal changes relax the muscles of the urinary tract, the growing uterus can prevent the bladder from emptying completely, and higher glucose levels in urine support bacterial growth.
Contamination from vaginal discharge is also more common during pregnancy and can produce a false positive. A midstream, clean-catch sample helps avoid this. When leukocytes are found, a urine culture is typically the next step to confirm whether a true infection is present, since the dipstick alone has only about 50% sensitivity for detecting significant bacteria in pregnant women.
What Happens After a Positive Result
A positive leukocyte finding paired with urinary symptoms like burning, urgency, or cloudy urine generally points toward a UTI. For a straightforward bladder infection in an otherwise healthy person, a short course of antibiotics, often one to three days, is the standard approach. Pain and burning tend to improve quickly once treatment starts. More complicated infections or kidney involvement may require a longer course of a week or more.
If you have leukocytes in your urine but no symptoms, the picture is different. The presence of white blood cells alone isn’t enough to diagnose a UTI, and it doesn’t automatically mean you need antibiotics. Infectious disease guidelines are clear that pyuria without symptoms is not, by itself, a reason for treatment. Your provider will look at the full picture, including your symptoms, culture results, and medical history, before deciding on next steps.
When no infection is found and leukocytes persist across multiple tests, further workup may include imaging of the kidneys and urinary tract, screening for sexually transmitted infections, or a review of your current medications to rule out drug-related inflammation.