What are the implications and next steps for a patient with a urinalysis positive for squamous epithelial cells?

Squamous Epithelial Cells in Urinalysis: Clinical Significance and Management

Primary Interpretation

Squamous epithelial cells in urinalysis primarily indicate specimen contamination from the distal urethra or genital region, not true urinary tract pathology, and should prompt consideration of specimen recollection if clinical suspicion for UTI remains high. 1

Understanding the Source

Squamous epithelial cells originate from:

• The distal third of the urethra (which is lined by squamous epithelium) 1
• The trigone area of the bladder 1
• The cervicovaginal region in women 1, 2

These cells are normal anatomic components and their presence does not indicate disease in most cases 1.

Clinical Significance for UTI Diagnosis

Impact on Specimen Quality

The presence of significant squamous epithelial cells alongside >10 WBCs suggests potential sample contamination rather than true infection. 1

Key evidence regarding contamination:

• Clean-catch specimens have a 27% contamination rate 1
• Bag specimens have a 65-68% contamination rate 1
• Catheterized specimens have only a 4.7% contamination rate 1

Effect on Urinalysis Accuracy

Squamous epithelial cells reduce the diagnostic accuracy of urinalysis for predicting bacteriuria. 3, 4

Specifically:

• When SECs are absent (<8 SECs/lpf): urinalysis predicts bacteriuria with sensitivity 75% and specificity 84% 3
• When SECs are present (>8 SECs/lpf): sensitivity increases to 86% but specificity drops to 70%, with overall reduced diagnostic odds ratio (17.5 vs 8.7) 3
• The positive likelihood ratio for bacteriuria drops from 4.98 to 2.35 when more than 8 SECs/lpf are present 3

Important caveat: Despite conventional teaching, squamous cells are poor predictors of urine culture contamination (AUC = 0.680), with 94% of catheterized samples containing squamous cells yet having no bacterial contamination 3, 5.

Recommended Management Algorithm

Step 1: Assess Clinical Context

If the urinalysis shows squamous epithelial cells alongside mixed bacterial flora, this indicates contamination rather than true UTI and does not require antimicrobial treatment. 6

Step 2: Determine Need for Recollection

When significant squamous epithelial cells are present and clinical suspicion for UTI remains high, recollect the specimen using a more reliable method. 1

Collection method hierarchy:

• First choice: Catheterization (sensitivity 95%, specificity 99%) 1
• Second choice: Properly cleansed clean-catch (reduces contamination from 23.9% to 7.8% with proper perineal cleansing) 1
• Avoid: Bag collection in pediatrics (65-68% contamination rate) 7, 6

Step 3: Special Populations

For febrile infants and children (2-24 months): If urinalysis suggests UTI (positive leukocyte esterase or nitrites), obtain culture via catheterization or suprapubic aspiration before initiating antibiotics 7.

For adults with persistent symptoms: Obtain midstream clean-catch specimen with proper perineal cleansing, or proceed directly to catheterization if initial specimen was heavily contaminated 6.

When to Consider Pathologic Squamous Cells

Atypical Squamous Cells (ASC)

Atypical squamous cells in urine are rare (0.3% of specimens) but clinically significant, with 31% subsequently diagnosed with malignancy. 8

Malignancies associated with urinary ASC:

• Squamous cell carcinoma of the bladder (25% of cases with adequate follow-up) 8
• Urothelial carcinoma with squamous differentiation (25% of cases) 8
• High-grade cervical squamous cell carcinoma (6% of cases) 8
• Endometrial adenocarcinoma with squamous differentiation (rare) 2

If atypical squamous cells are reported, the Bethesda System should be used for reporting, with appropriate follow-up including cystoscopy and pelvic examination in women. 7, 1

Common Pitfalls to Avoid

• Do not diagnose UTI based on contaminated specimens with squamous cells and mixed flora 6
• Do not assume squamous cells always indicate contamination—they are present in 94% of catheterized specimens 5
• Do not rely solely on squamous cell count to determine specimen adequacy for culture 3
• Do not overlook atypical squamous cells, which may indicate underlying malignancy requiring urologic and gynecologic evaluation 8

Practical Summary

For routine squamous epithelial cells: Consider specimen contamination if accompanied by mixed flora or >10 WBCs; recollect with proper technique if clinical suspicion for UTI persists 1, 6.

For atypical squamous cells: Pursue comprehensive urologic evaluation including cystoscopy and, in women, pelvic examination to exclude malignancy 8.