Comparison of Microbiological Methods for the Diagnosis of Urinary Tract Infections

Abstract

Objective: Urinary tract infections are the most frequent bacterial infections in adults and may be seen in all age groups and both genders. In this study, urine culture which is the gold standard diagnostic method of urinary tract infections is compared with Gram stain, Thoma counting chamber, nitrite reductase test and leukocyte esterase (LE) test in efficiency for rapid and reliable diagnosis of urinary tract infection. Methods: This study was performed in our laboratory between May 2010 and November 2010. 658 urine samples of patients with urinary tract infection symptoms from outpatient and inpatient clinics were included in the study. Urine samples were examined by Gram stain, leukocyte count in Thoma chamber, nitrit test and LE test, and cultured. Microorganisms were identified using conventional methods and API (R) (bioMerieux, Fransa) identification systems. Results: Cultures were found positive in 137 (20.8%) samples and 143 (21.7%) cultures were evaluated as contamination. For Gram stain, the results for sensitivity, specificity, false positivity and false negativity were 82.2%, 96.8%, 3.2%, and 17.8%, respectively. For Thoma counting chamber, the results were 78.8%, 81.5%, 18.5%, 21.2%, respectively. For nitrite reductase test they were 40.1%, 95.8%, 4.2%, 59.9%; and for LE test, they were 88.1%, 34.1%, 65.9%, 11.9%, respectively. Conclusions: Gram stain was found to be the most suitable method for rapid diagnosis of urinary tract infections compared to other diagnostic methods. False positive and false negative rates were low with very high sensitivity and specificity rates, besides ease of application.