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

Few Bacteria and Squamous Cells in Urinalysis Indicate Contamination, Not UTI

The presence of few bacteria and squamous epithelial cells in a urinalysis most likely represents contamination from the urethra or external genitalia during collection rather than a true urinary tract infection (UTI), especially when not accompanied by significant pyuria. 1

Understanding the Significance of Bacteria and Squamous Cells

• Squamous epithelial cells in urine samples typically indicate contamination during collection, as they are not normally present in properly collected specimens 1
• The presence of bacteria without significant pyuria is usually attributable to external contamination, asymptomatic bacteriuria, or rarely, very early infection before inflammation begins 1
• True UTI requires both bacteriuria and pyuria, as pyuria represents the host's inflammatory response to infection 1, 2

Diagnostic Criteria for UTI

• For a diagnosis of UTI, clinicians should look for:

  • Significant bacteriuria (≥50,000 CFU/mL of a single uropathogen) 2
  • Evidence of pyuria (≥10 WBCs/mm³ on enhanced urinalysis or ≥5 WBCs/HPF on centrifuged specimen) 1
  • Positive leukocyte esterase and/or nitrite test 2

• Low bacterial counts with few epithelial cells but without significant pyuria fall below diagnostic thresholds for UTI 1

Impact of Collection Method on Interpretation

• The method of urine collection significantly impacts interpretation: 1

  • Bag-collected specimens have high contamination rates (12-83%)
  • Clean-catch specimens have contamination rates of 0-29%
  • Catheterization or suprapubic aspiration provide the most reliable specimens

• Specimens with squamous epithelial cells are more likely to represent contamination, especially when obtained via non-invasive collection methods 1

Clinical Decision Making

• When few bacteria and epithelial cells are present without significant pyuria, no treatment is typically required in asymptomatic individuals 1
• Consider repeat specimen collection using a more reliable method if symptoms suggest UTI despite negative initial findings 1
• In symptomatic patients with dysuria, frequency, or urgency despite negative urinalysis, evaluate for other causes of urinary symptoms 1

Common Pitfalls to Avoid

• Treating based on the presence of bacteria alone without considering pyuria can lead to unnecessary antibiotic use 1, 2
• Ignoring specimen quality markers (epithelial cells) may result in overdiagnosis of UTI 1
• Multiple organisms typically indicate contamination rather than infection 1
• Delaying specimen processing can lead to falsely elevated bacterial counts due to bacterial growth at room temperature 1

Research Insights on Squamous Cells and Contamination

• Studies have shown that squamous epithelial cells are not reliable predictors of bacterial contamination, with an overall predictive value for contamination of only 21% in midstream clean-catch samples 3
• However, higher squamous epithelial cell counts may predict poorer performance of traditional urinalysis measures in predicting bacteriuria 4
• Recent research suggests sex-specific cutoffs for squamous epithelial cells that may help identify contaminated samples: 21.35 SEC/µL for women and 5.05 SEC/µL for men 5

Algorithmic Approach to Interpretation

1. Assess for pyuria (≥10 WBCs/mm³ or positive leukocyte esterase)

   • Present → Possible UTI, evaluate bacterial count
   • Absent → Likely contamination or asymptomatic bacteriuria 2, 1

2. Evaluate bacterial count

   • ≥50,000 CFU/mL of a single uropathogen → Likely UTI if pyuria present
   • <50,000 CFU/mL or multiple organisms → Likely contamination 2

3. Consider squamous epithelial cell count

   • High count → Increased likelihood of contamination
   • Low count → More reliable specimen 1, 5

4. If diagnosis remains unclear and symptoms persist:

   • Obtain new specimen via catheterization or suprapubic aspiration
   • Consider alternative diagnoses for urinary symptoms 1