What is the significance of squamous epithelial cells in urine?

Significance of Squamous Epithelial Cells in Urine

The presence of squamous epithelial cells in urine primarily indicates contamination from the periurethral, vaginal, or perineal area rather than a true urinary tract pathology. While these cells are commonly found in urine samples, they generally have limited diagnostic value for urinary tract infections but may affect the interpretation of other urinalysis findings.

Origin and Normal Presence

• Squamous epithelial cells in urine typically originate from the urethra, trigone area of the bladder, or contamination from the cervicovaginal region during collection 1
• These cells are commonly found in urine specimens, with studies showing presence in up to 94-96% of both catheterized and clean-catch midstream samples 2
• Their presence is considered a normal finding in most urine samples, especially in women 1, 2

Relationship to Sample Contamination

• Contrary to traditional belief, squamous epithelial cells alone are not reliable predictors of bacterial contamination in urine cultures 2, 3
• In one study, squamous cells were found in 96% of midstream samples but only 21% showed bacterial contamination 2
• More recent research demonstrates that squamous epithelial cell count is a poor predictor of urine culture contamination (area under ROC curve = 0.680) 3

Impact on Urinalysis Interpretation

• A urine sample with >10 WBCs and a significant number of epithelial cells should be considered potentially contaminated 1
• The presence of >8 squamous epithelial cells per low-power field may reduce the diagnostic performance of traditional urinalysis indicators for bacteriuria 3
• Samples with fewer squamous cells (<8/lpf) showed better specificity (84% vs. 70%) for predicting bacteriuria compared to samples with higher counts 3

Collection Methods and Contamination

• Collection method significantly affects contamination rates: clean-catch (27%), bag specimens (65-68%), and catheterized specimens (4.7%) 4
• Proper cleansing of the perineal area before collection can reduce contamination rates (7.8% with cleansing vs. 23.9% without) 4
• Catheterization provides more reliable specimens with higher sensitivity (95%) and specificity (99%) 1, 4

Clinical Significance in Special Circumstances

• Atypical squamous cells (ASCs) in urine are rare (0.3%) but clinically significant, as 31% of cases may later be diagnosed with squamous cell carcinoma 5
• ASCs may indicate underlying malignancy in the urinary tract or gynecologic tract and warrant further investigation 6, 5
• In rare cases, atypical squamous cells in urine may be the first sign of endometrial adenocarcinoma with squamous differentiation 6

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 4
• For proper interpretation of urine cultures with mixed flora and squamous cells, consider collection method, patient symptoms, and presence of pyuria 4
• In children with fever and suspected UTI, a positive culture with mixed flora and squamous cells should be confirmed by catheterization or suprapubic aspiration before treatment 4
• The presence of squamous epithelial cells should not be used as the sole criterion to reject a specimen, but should be considered alongside other urinalysis findings 7, 3