Urine Leukocytes (WBC)
Urine WBC· also: Pyuria, Urine Leukocytes, Leukocyte esterase
Clinical Overview
White blood cells (leukocytes) in urine — called pyuria — indicate inflammation or infection within the urinary tract. Leukocytes are detected on dipstick by leukocyte esterase (an enzyme released by neutrophils) and quantified on microscopy as WBC per high-power field. More than 5 WBCs per high-power field (WBC/HPF) on microscopy is the accepted threshold for significant pyuria.
Why This Test Matters
Pyuria is the most sensitive urinalysis marker for UTI — more sensitive than nitrites. Pyuria with positive nitrites provides high specificity for bacterial UTI. Pyuria without bacteriuria (sterile pyuria) is an important finding suggesting conditions other than common bacterial UTI: genitourinary tuberculosis (a classic cause of sterile pyuria in endemic areas), sexually transmitted infections (chlamydia, gonorrhea, mycoplasma — do not grow on standard urine culture), interstitial nephritis (often drug-induced), bladder tumor, kidney stones, or recent antibiotic treatment before culture was obtained. Pyuria combined with RBC casts on microscopy strongly suggests glomerulonephritis. The leukocyte esterase dipstick is approximately 75–90% sensitive and 95% specific for UTI when interpreted alongside nitrites.
Reference RangesWHO/IFCC standards
| Reference Range | Unit | Notes |
|---|---|---|
| 0 – 5 | WBC/HPF | <5 WBC/HPF = normal on microscopy |
Also reported in: WBC/HPF.
What Causes Abnormal Results?
High Urine WBC Causes
- Urinary tract infection (cystitis, pyelonephritis) — most common cause
- Sexually transmitted infections (Chlamydia trachomatis, Neisseria gonorrhoeae, Ureaplasma) — sterile pyuria
- Genitourinary tuberculosis — classic cause of sterile pyuria in endemic areas
- Interstitial nephritis (drug-induced: NSAIDs, antibiotics, PPIs; also autoimmune)
- Kidney stones (irritation of urothelium)
- Bladder tumor
- Vaginal contamination in women (squamous cells and WBCs from vaginal flora)
- Post-urological procedure (cystoscopy, catheterization)
- Viral cystitis (adenovirus, CMV in immunocompromised)
Low Urine WBC Causes
- Fewer than 5 WBC/HPF is normal and does not indicate infection
- Very dilute urine may reduce visible WBCs below detection threshold
Signs & Symptoms to Watch For
How to Prepare for This Test
Collect midstream clean-catch urine to minimize contamination. Women should clean the perineum carefully. Process within 2 hours or refrigerate — WBCs lyse rapidly, especially in dilute or alkaline urine. First morning urine has the highest WBC concentration for detection of sterile pyuria.
Factors That Can Affect Results
- Vaginal contamination in female samples — contains squamous epithelial cells and WBCs (false-positive leukocytes)
- Leukocyte esterase may be false-positive with: Trichomonas vaginalis, oxidizing cleaning agents
- False-negative leukocyte esterase: high glucose concentration (dilutes/inhibits enzyme), high protein, high specific gravity
- High vitamin C concentration can reduce leukocyte esterase sensitivity
- WBCs lyse rapidly in dilute or alkaline urine — delayed processing causes false-negative microscopy
Related Topics
Frequently Asked Questions
What is sterile pyuria and why is it important?
Sterile pyuria means white blood cells are present in urine (pyuria) but the standard urine culture is negative — no bacteria grow. This is not a false-positive finding; it indicates urinary tract inflammation from non-bacterial causes. The most important conditions causing sterile pyuria are: genitourinary tuberculosis (must be excluded in endemic areas or travellers — requires mycobacterial culture on 3 early morning urine samples), chlamydia and gonorrhea (STIs — require specific STI testing, not standard culture), interstitial nephritis (check for recent drug exposure), and prior antibiotic treatment (killed the bacteria before culture was taken). Sterile pyuria should never be dismissed — it requires specific investigation.
My elderly mother has pyuria on urinalysis but no symptoms — should she be treated?
Most likely no. Asymptomatic bacteriuria and asymptomatic pyuria are extremely common in the elderly — occurring in 10–50% of elderly women and 5–20% of elderly men — without any clinical significance. Treating asymptomatic pyuria in elderly patients leads to antibiotic overuse, selection of resistant organisms, Clostridioides difficile infection risk, and drug side effects. Treatment of asymptomatic bacteriuria in the elderly is not recommended by any major guideline. Only treat if your mother develops symptoms (dysuria, frequency, urgency, new confusion, fever) — or if she is about to undergo a urological procedure.