Diagnostic performance of routine urinalysis parameters in urinary tract infection

Abstract

Background: Urinary tract infection (UTI) is a common bacterial infection presenting from asymptomatic bacteriuria to severe disease. Early detection is essential, and urinalysis remains the most frequently used screening tool owing to its rapidity and low cost, although urine culture is the diagnostic gold standard. Dipstick tests such as leukocyte esterase (LE) and nitrite (NIT) are widely used, but their performance varies. This study assessed the diagnostic accuracy of LE, NIT, leukocyte count, and bacteriuria in predicting significant bacteriuria compared with urine culture.

Methods: This retrospective observational study included adult mid-stream urine samples processed in the Pathology and Microbiology Departments of FMMC Hospital, Mangalore (March, 2022). Of 3618 urinalysis samples, 306 had concurrent culture. Dipstick parameters (LE, NIT) and microscopic sediment findings (leukocyte count, bacteriuria) were recorded. Culture growth ≥10⁵ CFU/ml was taken as significant. Statistical analysis included sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), diagnostic accuracy, and kappa.

Results: Among 278 samples, females were slightly more represented. E. coli was the most common isolate (43.2%). Sixty-five percent showed >10⁵ CFU/ml growth. NIT was positive in 16%, while LE 3+ was the most frequent dipstick result. High leukocyte count (≥20 WBC/hpf) occurred in 37% and bacteriuria in 29%. High leukocyte count showed 43.4% sensitivity and 75% specificity. Combining ≥20 WBC/hpf with bacteriuria improved specificity (91.7%) and PPV (81.8%).

Conclusions: Routine urinalysis is useful as an initial screening tool, but microscopic sediment analysis is superior to dipstick testing. However, urine culture remains essential for definitive diagnosis.