What does an increase in bacteria and squamous cells in a urinalysis indicate?

Interpretation of Increased Bacteria and Squamous Cells in Urinalysis

The presence of increased bacteria and squamous cells in a urinalysis most commonly indicates specimen contamination rather than a true urinary tract infection, especially when not accompanied by significant pyuria (white blood cells). 1

Understanding the Significance of These Findings

• Squamous epithelial cells in urine samples typically indicate contamination from the urethra or external genitalia during collection, as they are not normally present in properly collected specimens 1
• Bacteria without significant pyuria is usually attributable to external contamination, asymptomatic bacteriuria, or rarely, very early infection before inflammation begins 1
• The presence of both bacteria and squamous cells together strongly suggests contamination during collection rather than a pathological process 2, 3

Diagnostic Criteria for True UTI

• True UTI requires both significant bacteriuria (≥50,000 CFU/mL of a single uropathogen) AND evidence of pyuria (≥10 WBCs/mm³ or positive leukocyte esterase) 4, 1
• The absence of pyuria in the presence of bacteriuria strongly suggests asymptomatic bacteriuria rather than infection 4
• Microscopic pyuria (>10 WBCs/high-power field) or a positive dipstick test for leukocyte esterase are not highly predictive of bacteriuria, but the absence of pyuria can exclude bacteriuria with a negative predictive value approaching 100% 4

Impact of Collection Method on Interpretation

• The method of urine collection significantly impacts interpretation, with non-invasive collection methods having higher contamination rates 1
• Clean-catch specimens have contamination rates of 0-29%, while bag-collected specimens have much higher contamination rates (12-83%) 1
• Catheterization or suprapubic aspiration provide the most reliable specimens with minimal contamination 1, 5

Quantitative Considerations

• Recent research shows that squamous epithelial cell counts above 21.35/μL for women and 5.05/μL for men are associated with a higher likelihood of mixed culture/contamination 6
• Bacterial counts must be interpreted in conjunction with clinical presentation and collection method 5
• The presence of multiple bacterial species (mixed flora) further supports contamination rather than infection 1

Clinical Decision Making

• When bacteria and squamous cells are present without significant pyuria in an asymptomatic individual, no treatment is typically required 1, 4
• In symptomatic patients, consider repeat specimen collection using a more reliable method before initiating treatment 1
• Urine culture may not be necessary for uncomplicated UTIs in outpatients but is recommended for recurrent UTIs, treatment failures, complicated UTIs, and inpatients 7

Common Pitfalls to Avoid

• Treating based on the presence of bacteria alone without considering pyuria can lead to unnecessary antibiotic use 1
• Ignoring specimen quality markers (squamous epithelial cells) may result in overdiagnosis of UTI 1
• Contrary to traditional teaching, studies show that squamous cells alone are a poor predictor of urine culture contamination (area under ROC curve = 0.680) 3
• Delaying specimen processing can lead to falsely elevated bacterial counts due to bacterial growth at room temperature 1

Special Considerations

• In rare cases, intracellular bacterial communities can be found within squamous cells, which may represent a different pathogenic mechanism rather than simple contamination 8
• Asymptomatic bacteriuria is common in certain populations (10-50% in long-term care facility residents) and should not be treated without symptoms 4