Squamous Cells in Urine: Clinical Significance and Management
Primary Recommendation
Squamous cells in urine typically indicate specimen contamination rather than pathology and do not require treatment—the appropriate response is to recognize contamination and recollect the specimen using proper technique if clinical suspicion for urinary tract infection remains high. 1, 2
Origin and Normal Presence
Squamous epithelial cells normally originate from three sources:
- Distal urethra and bladder trigone: The distal third of the urethra is dominated by squamous epithelium 3, 1
- Cervicovaginal contamination: Particularly common in women during specimen collection 1, 2
- Normal exfoliation: These cells are frequently present without pathologic significance 4
Clinical Interpretation
Contamination Indicator
The presence of significant squamous cells alongside >10 WBCs suggests sample contamination rather than true infection. 1, 2
- Squamous cells are poor predictors of urine culture contamination with limited diagnostic utility (area under ROC curve = 0.680) 5
- In one study, 94% of catheterized samples contained squamous cells, yet none had bacterial contamination 4
- Among midstream clean-catch samples with squamous cells, only 21% showed bacterial contamination 4
Impact on Urinalysis Performance
Squamous cells may predict reduced accuracy of traditional urinalysis measures:
- Samples with <8 SECs/lpf: Better predictive performance (sensitivity 75%, specificity 84%) 5
- Samples with >8 SECs/lpf: Reduced performance (sensitivity 86%, specificity 70%) 5
- The positive likelihood ratio for bacteriuria drops from 4.98 to 2.35 when >8 SECs/lpf are present 5
Collection Method Matters
Contamination rates vary dramatically by collection technique:
- Catheterized specimens: 4.7% contamination rate (sensitivity 95%, specificity 99%) 1, 2
- Clean-catch specimens: 27% contamination rate 1, 2
- Bag specimens: 65-68% contamination rate 1, 2
Proper perineal cleansing before collection reduces contamination from 23.9% to 7.8%. 1, 2
When to Recollect
Recollection is warranted when:
- Significant squamous cells present alongside mixed bacterial flora and clinical suspicion for UTI remains high 1, 2
- Initial specimen shows >10 SECs/mm³ with multiple organisms (≥2 organisms) 6
- Specimens with ≥10 SECs/mm³ have significantly more isolates (2 per culture) versus <10 SECs/mm³ (0.9 per culture) 6
Use catheterization for recollection when reliable results are essential, particularly in children with fever or when treatment decisions depend on accurate culture results. 2
Rare Pathologic Significance
While squamous cells usually indicate contamination, atypical squamous cells (ASCs) warrant further evaluation:
- ASCs occur in only 0.3% of urine specimens 7
- 31% of patients with ASCs in urine were subsequently diagnosed with malignancy 7
- Malignancies included: squamous cell carcinoma of bladder, urothelial carcinoma with squamous differentiation, or cervical squamous cell carcinoma 8, 7
- ASCs are defined as keratinizing cells with large hyperchromatic nuclei, high N/C ratio, and densely orangeophilic cytoplasm 7
If atypical squamous cells are identified, consider cystoscopic evaluation and pelvic examination (in women) to exclude underlying malignancy. 7
Practical Algorithm
- Review collection method: Was proper perineal cleansing performed? 1, 2
- Assess squamous cell quantity: >10 SECs/mm³ suggests contamination 6
- Evaluate clinical context:
- Recollect if needed: Use catheterization for most reliable results 1, 2
- If atypical squamous cells present: Pursue histologic evaluation and consider malignancy workup 7
Key Pitfall to Avoid
Do not reflexively treat presumed UTI based on urinalysis showing squamous cells with mixed flora—this combination strongly suggests contamination rather than true infection, and recollection with proper technique is the appropriate next step. 1, 2, 6