Evaluation of modified Wright-staining of urine sediment as a method for accurate detection of bacteriuria in dogs

Abstract

Objective: To compare the findings of light microscopic evaluation of routine unstained wet-mounted preparations and air-dried, modified Wright-stained preparations of urine sediment with results of quantitative aerobic bacteriologic culture of urine.

Design: Masked prospective study.

Sample population: 459 urine samples collected by cystocentesis from 441 dogs.

Procedure: Urinalyses and quantitative bacteriologic cultures of urine were performed. Unstained wet-mounted preparations and air-dried, modified Wright-stained urine sediment preparations were examined by light microscopy for the presence of bacteria.

Results: Compared with results of quantitative bacteriologic culture, routine unstained preparations and modified Wright-stained preparations had sensitivities of 82.4% and 93.2%, specificities of 76.4% and 99.0%, positive predictive values of 40.1% and 94.5%, negative predictive values of 95.8% and 98.7%, and test efficiencies of 77.3% and 98.0%, respectively. Compared with 74 samples that yielded growth on bacteriologic culture, the routine unstained method had concordance and misclassification rates of 39.2% and 60.8%, respectively, whereas the Wright-stained method had concordance and misclassification rates of 78.4% and 21.6%, respectively. Significant associations between each of occult blood in urine, pyuria, female sex, and lower urine specific gravity with bacteriuria detected by Wright-stained sediment examination and quantitative bacteriologic culture of urine were identified.

Conclusions and clinical relevance: Examination of modified Wright-stained preparations of urine sediment appeared to be a rapid, cost effective method that significantly improved the sensitivity, specificity, positive predictive value, and test efficiency of light microscopic detection of bacteriuria, compared with that of the routine unstained method.