This study compares the performance of urine dipstick alone with urine microscopy and with both tests combined as a screen for urinary tract infection (UTI) in febrile infants aged 1 to 90 days.
We queried the Intermountain Healthcare data warehouse to identify febrile infants with urine dipstick, microscopy, and culture performed between 2004 and 2011. UTI was defined as >50 000 colony-forming units per milliliter of a urinary pathogen. We compared the performance of urine dipstick with unstained microscopy or both tests combined (“combined urinalysis”) to identify UTI in infants aged 1 to 90 days.
Of 13 030 febrile infants identified, 6394 (49%) had all tests performed and were included in the analysis. Of these, 770 (12%) had UTI. Urine culture results were positive within 24 hours in 83% of UTIs. The negative predictive value (NPV) was >98% for all tests. The combined urinalysis NPV was 99.2% (95% confidence interval: 99.1%–99.3%) and was significantly greater than the dipstick NPV of 98.7% (98.6%–98.8%). The dipstick positive predictive value was significantly greater than combined urinalysis (66.8% [66.2%–67.4%] vs 51.2% [50.6%–51.8%]). These data suggest 8 febrile infants would be predicted to have a false-positive combined urinalysis for every 1 infant with UTI initially missed by dipstick screening.
Urine dipstick testing compares favorably with both microscopy and combined urinalysis in febrile infants aged 1 to 90 days. The urine dipstick test may be an adequate stand-alone screen for UTI in febrile infants while awaiting urine culture results.