What does the presence of squamous cells in a urinalysis indicate?

Significance of Squamous Cells in Urinalysis

The presence of squamous epithelial cells in a urinalysis typically indicates contamination from the urethra, trigone area of the bladder, or the cervicovaginal region during sample collection, and is not inherently pathological. 1

Origin and Normal Occurrence

• Squamous epithelial cells normally line the distal urethra and the trigone area of the bladder, as well as the cervicovaginal region in women 1
• The distal third of the urethra is dominated by squamous epithelium, while the proximal two-thirds contains transitional epithelium 2
• These cells commonly appear in urine samples, particularly in voided specimens from women 3

Clinical Significance and Interpretation

• A significant number of squamous epithelial cells alongside >10 WBCs suggests potential sample contamination 1
• The presence of squamous cells alone is a poor predictor of bacterial contamination in urine cultures (area under ROC curve = 0.680) 4
• In catheterized samples, 94% contain squamous cells despite having no bacterial contamination, indicating that squamous cells are a normal finding 3
• High numbers of squamous cells (>8 cells/low-powered field) may reduce the predictive performance of traditional urinalysis measures for detecting bacteriuria 4

Collection Method Considerations

• Collection method significantly affects contamination rates:
  • Clean-catch specimens: 27% contamination rate
  • Bag specimens: 65-68% contamination rate
  • Catheterized specimens: only 4.7% contamination rate 1
• Proper cleansing of the perineal area before collection can reduce contamination rates from 23.9% to 7.8% 1

Atypical Squamous Cells

• The presence of atypical squamous cells (ASCs) in urine is rare (0.3% of samples) but clinically significant 5
• ASCs are characterized by keratinizing cells with large hyperchromatic nuclei, high N/C ratio, and densely orangeophilic cytoplasm 5
• In 31% of cases with ASCs, subsequent histologic examination revealed squamous cell carcinoma of the bladder, urothelial carcinoma with squamous differentiation, or high-grade cervical SCC 5
• When atypical squamous cells are identified, further evaluation with colposcopy and directed biopsy may be warranted 2

Recommendations for Practice

• When significant squamous epithelial cells are present alongside mixed bacterial flora, consider recollection using a more reliable method if clinical suspicion for UTI remains high 1
• Catheterization provides more reliable specimens with higher sensitivity (95%) and specificity (99%) 1
• In women with atypical squamous cells in urine cytology, consider pelvic examination to rule out cervical pathology 5
• The Bethesda System should be used for reporting urine cytology results, with appropriate follow-up for any epithelial cell abnormalities 2

Special Considerations

• Rarely, squamous cells in urine may contain intracellular bacterial communities, which can be visualized with Sternheimer-Malbin staining and brightfield microscopy 6
• In HIV-infected women, more frequent cervical screening may be needed due to higher risk of squamous intraepithelial lesions 2
• In patients with neurogenic lower urinary tract dysfunction, the presence of squamous cells alongside hematuria may warrant cystoscopic evaluation 2