White blood cells (WBCs) are a central component of the body’s immune system, tasked with fighting off infection and foreign invaders. Normally, only a minimal amount of these cells should be present in a urine sample. A high concentration of WBCs signals that the immune response has been activated within the urinary tract or an adjacent area. This elevation indicates inflammation or infection along the path from the kidneys, through the ureters and bladder, and out the urethra. A high WBC count always prompts further investigation to determine the precise source of the immune activation.
Understanding the Levels: What is Pyuria?
The clinical term for an abnormally high count of white blood cells in the urine is pyuria. Diagnosis occurs via urinalysis, using either a chemical dipstick test to detect leukocyte esterase or microscopic examination. A normal urine sample typically contains five or fewer white blood cells per high-power field (WBC/HPF). Pyuria is generally defined as a count greater than 10 WBC/HPF in centrifuged urine, signifying a definite inflammatory process. Pyuria alone does not identify the cause, but it directs healthcare providers toward seeking an underlying issue.
The Most Common Reason: Bacterial Infection
The most frequent reason for elevated white blood cells in urine is a bacterial urinary tract infection (UTI). When bacteria, such as E. coli, enter the system, the body initiates an immune response by rapidly dispatching WBCs to the site of invasion. These immune cells then migrate through the lining of the urinary tract and into the urine, where they are detected during testing.
Infections can occur in the lower urinary tract, known as cystitis or a bladder infection, which often presents with symptoms like a burning sensation during urination, frequent urges to urinate, and cloudy or strong-smelling urine. Pyelonephritis is a more serious upper urinary tract infection of the kidney. This infection typically causes symptoms that include fever, chills, nausea, vomiting, and pain in the flank or back. The body’s mobilization of white blood cells to combat the bacteria results in a significant increase in the WBC count found in the urine.
Other Sources of Inflammation
While bacterial UTIs are the most common cause, a high WBC count can also result from non-bacterial infections or sources of inflammation. Certain sexually transmitted infections (STIs), such as Chlamydia trachomatis and Neisseria gonorrhoeae, can inflame the urethra and cause pyuria, even if standard bacterial cultures are negative. In men, inflammation of the prostate gland, known as prostatitis, can lead to WBCs spilling into the urine.
In women, adjacent inflammatory conditions like vaginitis may contaminate a urine sample, leading to a falsely elevated count if not collected properly. Non-infectious irritants, such as kidney or bladder stones, can mechanically irritate the lining of the urinary tract, triggering a localized immune response and the release of white blood cells. A distinct category called aseptic pyuria describes the presence of WBCs without detectable bacteria, which can be linked to conditions like interstitial cystitis, certain medications, or systemic inflammatory diseases.
Next Steps: Further Testing and Treatment
When a high white blood cell count is detected, the immediate next step is a urine culture and sensitivity test. This specialized test identifies the type of bacteria or other pathogen present and determines which antibiotics will be most effective against it. If pyuria is accompanied by signs of a bacterial infection, antibiotic therapy is typically initiated promptly, often using broad-spectrum drugs while waiting for the culture results.
If the urine culture returns negative for bacteria, further investigation is necessary to explore the possibility of a non-bacterial cause. This may involve specific tests for STIs or tuberculosis, or imaging studies like an ultrasound or CT scan to check for kidney stones or structural abnormalities. Treatment then focuses on managing the underlying condition, which could range from targeted antibiotics for an STI to procedures for removing obstructive kidney stones or medication management for inflammatory conditions.