WBC Count and Pus Cells in Urinalysis: Are They the Same?
Yes, in urinalysis, white blood cell (WBC) count and pus cells refer to the same thing—they are synonymous terms for leukocytes present in the urine. The term "pus cells" is simply a colloquial or older terminology for white blood cells detected during microscopic examination of urine.
Understanding the Terminology
The presence of WBCs in urine is called pyuria, which literally means "pus in urine." When laboratory reports mention either "WBC count" or "pus cells," they are both describing the number of white blood cells visible under microscopic examination. These cells indicate inflammation or infection in the urinary tract 1, 2, 1.
Clinical Significance and Diagnostic Thresholds
The interpretation of WBC/pus cell counts depends on several factors:
Standard Diagnostic Criteria
For urinary tract infection diagnosis, pyuria is defined as ≥10 WBCs per high-power field (HPF) in centrifuged urine specimens 2. However, this threshold varies based on:
- Method of analysis: Manual microscopy typically uses ≥8 WBC/HPF, while automated systems analyzing uncentrifuged urine may use different cutoffs 3
- Urine concentration: In dilute urine (specific gravity <1.015), a threshold of ≥3 WBC/HPF is appropriate, while concentrated urine (≥1.015) requires ≥6 WBC/HPF 4
- Age of patient: Pediatric thresholds may differ, with some studies suggesting ≥10 WBC/μL for infants 5
Important Clinical Caveats
The presence of pyuria (elevated WBC/pus cells) does not automatically confirm a urinary tract infection. Several critical points:
- Pyuria has relatively low positive predictive value for bacteriuria but excellent negative predictive value approaching 100% 1
- A negative urinalysis for WBCs effectively excludes UTI, making it useful as a rule-out test 2, 6
- Asymptomatic bacteriuria is common (10-50% in elderly populations) and frequently shows pyuria without requiring treatment 1
- In neutropenic patients, significant bacteriuria may occur without pyuria 1
Practical Application
When interpreting urinalysis results:
- WBC/pus cells ≥10/HPF + symptoms = likely UTI requiring culture 2
- WBC/pus cells <10/HPF = UTI unlikely, can exclude urinary source 1
- Always correlate with clinical symptoms—pyuria alone in asymptomatic patients should not trigger treatment 2
- Leukocyte esterase on dipstick is an indirect measure of WBCs and has high sensitivity (72-97%) but lower specificity 7
The key takeaway: whether your laboratory report states "WBC count" or "pus cells," these terms are interchangeable and both refer to the number of white blood cells detected in the urine specimen.