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Reference: Pediatrics 2014 Apr 28 early online (level 2 [mid-level] evidence)
Serious bacterial infections occur in about 9% of febrile infants aged 1-90 days, with urinary tract infection (UTI) being the most common diagnosis (Pediatrics 2004 Jun;113(6):1662). UTI screening methods include urine dipstick and microscopy of centrifuged urine. Urine dipstick is a relatively simple procedure that can be performed in office settings with minimal training, whereas microscopic examination of urine requires more extensive training. A recent retrospective diagnostic cohort study evaluated both urine dipstick and microscopy for detection of UTI in 6,536 febrile infants aged 1-90 days.
All infants had urine samples obtained by catheterization. The urine dipstick testing used colorimetric interpretation by a semiautomated urine chemistry analyzer. In addition to the comparison with microscopy, a combined analysis was performed, with a positive result defined as positive findings on either urine dipstick or microscopy. The reference standard was urine culture, with UTI defined as presence of > 50,000 colony-forming units/mL of any urinary pathogen. A total of 6,394 infants (98%) with unequivocal urine cultures were included in the analysis.
The prevalence of UTI was about 12% by reference standard. For detection of UTI in the overall analysis, all tests had negative predictive value > 98%. The urine dipstick testing had sensitivity 90.8%, specificity 93.8%, positive predictive value (PPV) 66.8%, and negative predictive value (NPV) 98.7%. Microscopy analysis had sensitivity 90.3%, specificity 91.3%, PPV 58.6%, and NPV 98.6%. The combined urine dipstick and microscopy analysis had sensitivity 94.7%, specificity 87.6%, PPV 51.2%, and NPV 99.2%. The addition of microscopy to urine dipstick was estimated to produce 8 false positive diagnoses of UTI for every diagnosis missed with urine dipstick alone. In 53 infants with subsequent UTI diagnosis after negative urine dipstick, no adverse outcomes were observed.
Urine dipstick testing is a rapid and inexpensive test for detection of UTI that does not require specialized training. These new findings demonstrate that a negative result on urine dipstick testing may rule out UTI in infants < 90 days old. Although adding microscopy analysis to urine dipstick testing resulted in a higher negative predictive value, this must be weighed against an increased number of false positives with combined analysis, which can lead to additional use of healthcare resources and potentially increased antibiotic exposure. Taken together, these data support urine dipstick testing without microscopy for detection of UTI in febrile infants while waiting for urine culture results.
For more information see the Fever without apparent source in infants less than 3 months old topic in DynaMed.