Is a urinalysis (UA) showing moderate leukocyte esterase, 7-10 white blood cells (WBCs), greater than 20 epithelial cells, and 4+ bacteria indicative of a urinary tract infection (UTI) or contamination?

Urinalysis Interpretation: Contamination vs. UTI

This specimen is most likely contaminated and should not be used to diagnose or treat a UTI.

The presence of >20 epithelial cells is the critical finding that indicates specimen contamination, regardless of other urinalysis parameters. 1

Key Diagnostic Reasoning

Why This Represents Contamination

• High epithelial cell count (>20) is the hallmark of a contaminated specimen, as epithelial cells originate from the skin and vaginal/urethral surfaces during collection, not from the bladder 1
• The combination of bacteria (4+) with high epithelial cells suggests skin flora contamination rather than true bladder infection 2
• Even in disease-free women using ideal clean-catch technique, bacteria can be present in 62.5% of specimens, and this increases to 77.5% with non-clean collection 2

Why the Other Findings Are Unreliable Here

• Moderate leukocyte esterase and 7-10 WBCs can occur in 27.5-50% of women without UTI, even with proper collection technique 2
• The presence of pyuria (WBCs) has relatively low predictive value for actual UTI when specimen quality is poor 3
• Leukocyte esterase has only 78% specificity, meaning false positives are common, particularly in contaminated specimens 4

Recommended Action

If strong clinical suspicion for UTI exists (fever, dysuria, urgency, frequency, gross hematuria), obtain a properly collected specimen before making treatment decisions. 3, 1

Proper Specimen Collection

• For cooperative women: perform in-and-out catheterization to obtain an uncontaminated specimen 3
• For men: use midstream clean-catch or freshly applied clean condom catheter with frequent monitoring 3
• Do not treat based on this contaminated specimen 1

Clinical Decision Algorithm

1. Assess for specific UTI symptoms: dysuria, frequency, urgency, fever >100.4°F, gross hematuria, or suspected urosepsis 3, 1
2. If symptomatic: Obtain properly collected specimen (catheterized for women if needed) 3
3. Repeat urinalysis on new specimen: If still shows high epithelial cells, catheterization is mandatory for definitive diagnosis 1
4. Only proceed to culture if: Pyuria ≥10 WBCs/HPF OR positive leukocyte esterase OR positive nitrite on the clean specimen 3, 4
5. If asymptomatic: Do not pursue further testing or treatment, as asymptomatic bacteriuria should not be treated 3, 4

Critical Pitfalls to Avoid

• Never treat based on urinalysis from a contaminated specimen (>20 epithelial cells indicates contamination) 1
• Do not assume all positive cultures represent infection—distinguish true UTI from asymptomatic bacteriuria, especially given the 10-50% prevalence of asymptomatic bacteriuria in certain populations 3, 4
• Avoid treating non-specific symptoms (confusion, functional decline, low-grade fever alone) as UTI in older adults without specific urinary symptoms 1, 4
• Remember that negative leukocyte esterase and nitrite together have excellent negative predictive value (>99.7%) for ruling out UTI, but positive results in contaminated specimens are meaningless 4, 5