Urine Specimen Contamination and Pathology

Epithelial Cell Types and Clinical Significance

The presence of epithelial cells in urine primarily serves as a marker of specimen contamination rather than disease, with squamous epithelial cells indicating contamination from the distal urethra or genitourinary tract, while renal tubular epithelial cells (RTECs) may indicate upper urinary tract pathology 1, 2
Squamous epithelial cells originate from the distal urethra, bladder trigone, or cervicovaginal contamination during collection, and are the most common type seen in routine urinalysis, typically indicating contamination rather than pathology 1, 2
Transitional (Urothelial) Epithelial Cells arise from the urinary tract lining and when atypical, may indicate urothelial neoplasia and require cytologic evaluation using standardized reporting systems 3, 4, 5, 6
Renal Tubular Epithelial Cells (RTECs) contain nephron-specific proteins and indicate upper urinary tract pathology 3

The collection method dramatically affects contamination rates and specimen reliability, with catheterized specimens having a 4.7% contamination rate, clean-catch midstream having a 27% contamination rate, and bag specimens having a 65-68% contamination rate 1, 2
Proper perineal cleansing reduces contamination from 23.9% to 7.8% 1, 2

When significant squamous epithelial cells are present alongside mixed bacterial flora, recollect using catheterization if clinical suspicion for UTI remains high 1, 2
In children with fever and suspected UTI, confirm any positive culture showing mixed flora and squamous cells by catheterization or suprapubic aspiration before initiating treatment 1
Assess collection method first, quantify squamous epithelial cells, evaluate in context, and consider patient symptoms, presence of pyuria, and bacterial growth pattern 1, 2

The International Consultation on Urologic Disease (ICUD) recommends standardized reporting using terminology similar to the Bethesda System for atypical urothelial cells 4, 5, 6
Atypical urothelial cells should be substratified into two classes with different follow-up implications, including atypical urothelial cells of undetermined significance and atypical urothelial cells that cannot rule out high-grade carcinoma or favor neoplasm 4, 5, 6