COMPARISON OF LABORATORY METHODS FOR THE DIAGNOSIS OF URINARY TRACT INFECTION
Abstract
Introduction: Urinary Tract Infection (UTI) is most frequent bacterial infection.Conventional urine culture is widely used for its diagnosis. This method is time consuming, expensive and patients are often treated before results are available. Dipsticks Nitrite Test (NT), Leucocyte Esterase (LET) and microscopic examination are commonly used primarily to predict the outcome of urinary tract infection.
Objective: To compare reagent strip testing with microscopy and culture on different medias to identify significant bacteriuria.
Methods: 500 samples were tested by semi-quantitative culture on cysteine lactose electrolyte deficient agar (CLED) with Andrade indicator, Mac conkey agar , Nutrient agar, microscopic examination of urine for significant pyuria, dipstick LET and NT. Culture was used as gold standard to evaluate the performance of direct microscopy and dipstick tests
Results: Out of 500 urine sample 162(32.4%) were culture positive , out of these 162 samples 100(61.7%) samples showed significant bacteriuria (>105 CFU/ml). Sensitivity, specificity, positive predictive value (PPV)and negative predictive value (NPV)of the dip-stick LET were 71.6%, 75.7%, 58.5%, and 84.7% respectively; those of the dip-stick NT were 59.2%, 84.0%, 64%, and 81%respectively; and those for microscopic significant pyuria detection were 66%, 81.3%,62.9% and 83.3% respectively. Highest sensitivity (87.6%) and NPV (93.1%) was obtained on combining microscopy and dip-stick LET and NT .
Escherichia coli was the most common organism isolated (n75=46.3%).
Conclusion: Study suggests that positive cultures cannot be accurately predicted by single method, but Combined use of all three methods have > 90% prediction (NPV) for negative culture. Use of CLED agar with Andrade indicator proven to be useful as primary medium & helped to reduce the plate burden & work load
