Is primary sensitivity testing on urine samples valid?

One thousand eight hundred urine specimens were examined prospectively to determine the validity of primary sensitivity testing. Microscopic criteria assessing pyuria and microorganisms were developed for predicting the presence of urinary tract infection and thus suitability for direct sensitivity testing. The criteria selected gave a positive predictive value of 74.6% and a negative predictive value of 99.5%. Zone diameters by primary and standardized secondary methods were compared for each urinary pathogen to each antibiotic tested. Percentage agreement between primary and secondary sensitivity results varied between 100% for Enterobacteriaceae tested against Gentamicin to 95.2% for Enterococcus faecalis tested against Ampicillin. Seventeen discrepancies between primary and secondary test results were observed (error 2.0%) with only 3 of potential clinical significance (primary sensitive, secondary resistant). Although primary sensitivity testing has limitations, our study indicates that the results are, in the vast majority of cases, in agreement with secondary testing, and are probably adequate for the clinical management of uncomplicated urinary tract infections. Furthermore, as primary testing rarely produces false resistant results it may permit earlier modification of initial empiric therapy.