What does the presence of more than 10 epithelial cells in a urinalysis (UA) indicate?

Epithelial Cells >10 in Urinalysis: Specimen Contamination

More than 10 epithelial cells per high-power field (or >1% epithelial cells) in a urinalysis indicates specimen contamination with periurethral or vaginal flora, rendering the sample unreliable for diagnosing urinary tract infection. 1

What This Finding Means

The presence of >10 epithelial cells per low-power field (or >10 epithelial cells/HPF) signals that the urine specimen was contaminated during collection, typically from inadequate perineal cleaning or improper collection technique 1. This contamination makes interpretation of other urinalysis findings unreliable, particularly:

• White blood cell counts become uninterpretable - A specimen with >10 WBCs AND significant epithelial cells must be considered contaminated 1
• Bacterial presence is likely from skin/vaginal flora rather than true bladder infection 1, 2
• Culture results are unreliable - Specimens with ≥10 epithelial cells/mm³ have significantly higher rates of mixed growth (53% vs 22% in clean specimens) 2

Why Epithelial Cells Indicate Contamination

Epithelial cells in urine originate from the urethra, vagina, or perineal skin—not from the bladder 1, 3. Their presence in high numbers indicates the specimen was contaminated with periurethral flora during collection 1. Studies show that specimens with <10 epithelial cells/mm³ had fewer isolates (0.9 per culture) compared to specimens with ≥10 epithelial cells/mm³ (2 isolates per culture) 2.

Critical Clinical Implications

Do not make treatment decisions based on contaminated specimens 1. The combination of pyuria with high epithelial cells has exceedingly low positive predictive value for actual UTI 4. Clinical laboratories may incorrectly report renal tubular epithelial cells as squamous epithelial cells, further complicating interpretation 3.

Proper Management Algorithm

Step 1: Recognize the Contaminated Specimen

• Epithelial cells >10/HPF = contaminated specimen 1
• Do not proceed with culture or treatment based on this specimen 1

Step 2: Obtain a Proper Specimen

For women: 1, 4

• Perform urethral catheterization (in-and-out) for definitive specimen
• Catheterization has 95% sensitivity and 99% specificity 1
• Alternative: Supervised midstream clean-catch with proper perineal cleaning

For men: 4

• Retract foreskin if uncircumcised to expose glans penis 1
• Midstream clean-catch with proper technique
• If phimosis present, catheterization may be required 1

For children <2 years: 1

• Urethral catheterization or suprapubic aspiration are methods of choice 1
• Bag collection has 12-83% false-positive rate and 85% chance that positive culture is false positive 1
• Any positive bag specimen requires confirmation by catheterization 1

Step 3: Process Specimen Correctly

• Process within 1 hour at room temperature or 4 hours if refrigerated 4
• Request microscopic examination, not just dipstick 1, 4

Common Pitfalls to Avoid

Never treat based on contaminated specimens - Even if the patient has symptoms, a contaminated specimen cannot reliably confirm or exclude UTI 1, 4. The false-positive rate for bag-collected specimens can reach 83%, and assuming 5% UTI prevalence, 85% of positive cultures from bag specimens are false positives 1.

Don't assume clean-catch is adequate - Studies show that even "ideal" midstream clean-catch technique in disease-free women resulted in abnormal urinalysis indices in 27.5-62.5% of cases 5. Culture contamination occurred in 63% even with ideal technique 5.

Recognize that epithelial cells predict mixed growth - Of specimens with ≥10 epithelial cells/mm³, 53% showed mixed growth on culture compared to only 22% in specimens without contamination 2.

Special Considerations

In Respiratory Specimens (BAL/PSB)

The >1% epithelial cell threshold also applies to bronchoscopic specimens, where >1% epithelial cells or 10 epithelial cells per low-power field suggests heavy oropharyngeal colonization, making the specimen unreliable 1.

In Pediatric Patients

Contamination rates for clean-catch specimens in children range from 0-29%, but bag collection has dramatically higher false-positive rates (12-83%) 1. For febrile infants <1 year, catheterization or suprapubic aspiration is strongly recommended 1.

When Clinical Suspicion Remains High

If strong clinical suspicion for UTI persists despite contaminated specimen (fever >38.3°C, dysuria, urgency, frequency, gross hematuria), obtain a properly collected specimen via catheterization before making treatment decisions 4. Do not empirically treat based on contaminated results 4.