What does the presence of squamous epithelial cells in urine indicate?

Squamous Epithelial Cells in Urine: Clinical Significance

The presence of squamous epithelial cells in urine primarily indicates contamination from the urethra or external genitalia during sample collection and generally does not indicate pathology. 1

Understanding Squamous Epithelial Cells in Urine

Squamous epithelial cells are normally found in:

• The distal urethra (especially the distal third which is dominated by squamous epithelium)
• External genitalia
• Vagina in women

Interpretation of Findings

• Sample Quality Indicator: The presence of squamous epithelial cells suggests upper airway secretion contamination during collection 1
• Threshold for Concern: Epithelial cells >5% suggest a suboptimal sample, and cellular patterns should be interpreted with caution 1
• Contamination vs. Pathology:
  • High numbers of squamous cells (≥10 SEC/mm³) are associated with more bacterial isolates per culture (2 isolates vs 0.9) 2
  • However, the presence of squamous cells alone is a poor predictor of urine culture contamination (area under ROC curve = 0.680) 3

Clinical Implications

When Squamous Cells Are Normal

• Routine finding in many urine samples (found in 94-96% of samples in some studies) 4
• More commonly seen in voided specimens than catheterized specimens
• More common in female patients due to anatomical considerations

When Squamous Cells May Warrant Further Investigation

1. Atypical Squamous Cells (ASCs):

   • Keratinizing cells with large hyperchromatic nuclei, high N/C ratio, abnormal shapes
   • Though rare (0.3% of urine specimens), ASCs may indicate underlying malignancy in 31% of cases 5
   • May be associated with:
     • Squamous cell carcinoma of the bladder
     • Urothelial carcinoma with squamous differentiation
     • High-grade cervical squamous cell carcinoma 5

2. Impact on Urinalysis Interpretation:

   • Samples with >8 squamous cells/low-power field show reduced specificity (70% vs 84%) for predicting bacteriuria compared to samples with fewer squamous cells 3
   • May affect the reliability of other urinalysis parameters

Recommendations for Clinical Practice

1. For Routine Urinalysis:

   • Document the presence and quantity of squamous epithelial cells
   • Consider repeat collection if excessive squamous cells are present, especially when evaluating for infection
   • Use proper collection techniques (mid-stream clean catch) to minimize contamination

2. For Atypical Squamous Cells:

   • Further investigation is warranted, including potential cystoscopy and imaging
   • Consider gynecologic examination in women to rule out cervical pathology 5

3. For Diagnostic Accuracy:

   • When squamous cells are abundant, interpret other urinalysis parameters with caution
   • Consider catheterized specimen if a clean sample is essential for diagnosis

Common Pitfalls

1. Misinterpreting normal contamination as pathological: Most squamous cells represent normal contamination during collection

2. Ignoring atypical squamous cells: While rare, atypical squamous cells with abnormal nuclear features require follow-up

3. Over-reliance on squamous cell count to predict contamination: Studies show squamous cell counts alone are poor predictors of bacterial contamination 3, 4

4. Failing to consider the entire clinical picture: Interpretation should always consider clinical symptoms, other urinalysis findings, and patient history

Remember that while squamous epithelial cells generally indicate sample contamination, atypical squamous cells with concerning features should prompt further investigation to rule out underlying malignancy.