Can the presence of squamous cells in a urinalysis (urine analysis) indicate contamination?

Presence of Squamous Cells in Urinalysis as an Indicator of Contamination

Yes, the presence of squamous cells in a urinalysis is a potential indicator of urine specimen contamination, though this relationship is not as strong or reliable as commonly believed. 1, 2

Understanding Squamous Cells in Urine Specimens

• Squamous epithelial cells (SECs) in urine typically originate from the distal urethra, vagina (in women), or skin during collection, and their presence has traditionally been associated with contamination 1, 3
• However, research shows that SECs are actually a poor predictor of bacterial contamination in urine cultures, with one study finding only a 21% predictive value for contamination in midstream clean-catch samples 1
• Squamous cells were found in 94-96% of both catheterized and midstream samples in one study, yet contamination rates varied significantly between collection methods 1

Relationship Between Squamous Cells and Specimen Quality

• Higher numbers of squamous cells (>8 SECs/low-powered field) may predict poorer performance of traditional urinalysis measures in detecting bacteriuria 2
• The presence of squamous cells along with multiple bacterial species or low colony counts (<50,000 CFU/mL) is more indicative of contamination than squamous cells alone 4, 5
• A urine sample with more than 10 WBCs and a significant number of epithelial cells should be considered contaminated, requiring improved collection techniques 6

Collection Methods and Contamination Rates

• Contamination rates vary significantly by collection method, with bag collection showing the highest rates (22-68%) compared to midstream clean-catch (8-27%) 6
• Catheterization and suprapubic aspiration provide the most reliable specimens with minimal contamination 6, 4
• Even with proper midstream clean-catch technique, some degree of squamous cell presence is expected and does not automatically invalidate results 1, 2

Clinical Implications and Best Practices

• When evaluating a urinalysis with squamous cells:
  • Consider the collection method used 6, 4
  • Look for other indicators of contamination (mixed bacterial flora, low colony counts) 4, 5
  • Assess the clinical context and presence of other urinalysis findings (pyuria, bacteriuria) 4, 5
• For definitive diagnosis of UTI, both pyuria and bacteriuria should be present, along with a significant colony count (≥50,000 CFU/mL) of a single uropathogen 4, 6

Common Pitfalls to Avoid

• Do not reject or discount urinalysis results based solely on the presence of squamous cells 1, 2
• Avoid over-reliance on squamous cell count as the sole determinant of specimen quality 2
• Remember that laboratory technicians may sometimes misidentify renal tubular epithelial cells as squamous cells, potentially affecting interpretation 7
• Written instructions alone for proper clean-catch technique may not significantly reduce contamination rates 8