There’s a reason general primary care has evolved to diagnose and treat uncomplicated urinary tract infections over the phone: the patient is the authority, not any test we order.
We’ve tried relying upon some constellation of the urinalysis, the urine microscopic examination, and, finally, the urine culture. Each of these has limitations, although, in many settings, the culture result has been the gold standard. However, this culture result, some quantification of the number of colony-forming units, is also somewhat of an arbitrary diagnostic – an arbitrary numerical cut-off must be used, with its own implications for sensitivity and specificity.
This brief clinical microbiology article evaluates the urine culture as a gold standard for the diagnosis of UTI by comparing it with polymerase chain reaction-based methods for measuring the presence of pathogenic bacteria. Based on 86 asymptomatic women and 220 general practice women complaining of UTI symptoms, these authors compared the number of positive culture results with positive PCR results. Of this sample, 149 had positive cultures for e. coli, while 211 patients had positive PCR for e. coli. Finally, combining the culture results – which identified other pathogens, as well – with the PCR for e. coli, 216 of 220 symptomatic women had pathogenic bacteria identified. In the control cohort, there were similar numbers of positive culture and PCR results – ~10% in each, which these authors feel accurately reflects the general rate of asymptomatic bacteruria in the general population.
These data correlate nicely with similar findings demonstrating a negative urine culture does not exclude clinical improvement while on antibiotics, and thus the reasonable conclusion we ought simply treat appropriate symptomatic patients without specifically relying on testing.
“Women with symptoms of a urinary tract infection but a negative urine culture: PCR-based quantification of Escherichia coli suggests infection in most cases”
http://www.clinicalmicrobiologyandinfection.com/article/S1198-743X(17)30209-4/abstract