Urinary leukocytes (white blood cells in urine) are a key marker of infection or inflammation in the urinary tract. Normally, very few white blood cells pass into the urine. When infection, inflammation, or injury is present in the kidneys or lower urinary tract, white blood cells migrate to the site and some spill into the urine.
Leucocyte esterase — an enzyme produced by white blood cells — is detected on dipstick urinalysis as a proxy for white blood cells. Microscopy provides a direct count. Elevated urinary leukocytes (pyuria) alongside positive nitrites and clinical symptoms strongly suggest a UTI. Sterile pyuria (white cells without bacteria) can indicate interstitial nephritis, tuberculosis of the urinary tract, or chlamydial infection.
FAQs
What is sterile pyuria?
White cells in urine without bacterial growth on standard culture. Causes include urinary tuberculosis (needs specific TB culture), chlamydial urethritis (urethral swab needed), interstitial nephritis, kidney stones, and contamination.
Can vaginal discharge cause false positive leucocytes?
Yes. Vaginal secretions in a poorly collected midstream sample can produce elevated leucocytes and squamous cells without true UTI. Midstream clean-catch technique and presence of many squamous cells suggests contamination.
How is leucocyte esterase related to white cells?
Leucocyte esterase is an enzyme released by white blood cells. The dipstick tests for this enzyme as a proxy for urinary leukocytes. Microscopy directly counts white cells and is more specific.
Can kidney disease cause white cells in urine?
Yes. Glomerulonephritis, interstitial nephritis, and urological tumours can produce white cells in urine without bacterial infection. Characterising the type of cells (neutrophils, eosinophils) on microscopy helps guide diagnosis.
