Dipstick Test Effective Initial Screen for UTI in Infants

Jenni Laidman

May 01, 2014

A dipstick test alone may be the best initial screen to test for urinary tract infections (UTIs) in febrile infants, the authors of a study published online April 28 in Pediatrics conclude.

Previous studies have demonstrated that dipstick tests work well for children aged 2 years and older. Unlike microscopic analysis, they require neither special training nor a certified laboratory. Moreover, some studies have questioned the added benefit of microscopic analysis, but those studies included few infants.

Therefore, Eric W. Glissmeyer, MD, adjunct instructor, Department of Pediatrics, University of Utah, Salt Lake City, and colleagues compared the performance of a urine dipstick test alone with unstained microscopy alone, as well as dipstick plus unstained, for the detection of UTI among 6394 febrile infants aged 1 to 90 days.

For the analysis, the researchers used diagnostic data from the Intermountain Healthcare Enterprise Data Warehouse, which treats some 90% of infants in Utah. Screening analyses were confirmed by culture, with a positive test defined as growth of one or more urine pathogens, each with 50,000 or more colony-forming units per milliliter.

Of the infants tested, 770 (12%) were diagnosed with UTI.

Although combining urinalysis with dipstick led to the higher negative predictive value (NPV) of 99.2% (95% confidence interval [CI], 99.1% - 99.3%) compared with the NPV of dipstick alone (98.7; 95% CI, 98.6% -98.8%; P < .003 for the comparison), the combined analysis lost ground when the authors assessed the positive predictive value (PPV) of each test. The dipstick PPV was 66.8% (95% CI, 66.2% - 67.4%) compared with 51.2% (95% CI, 50.6% - 51.8%; P < .001 for the comparison) for the combined analysis. The dipstick PPV of 66.8% was also better than the PPV for microscopic analysis alone (58.6%; 95% CI, 58.0% - 59.2%; P < .001 for the comparison).

The authors estimate that adding microscopy to dipstick testing leads to 8 false-positive diagnoses for every UTI missed by dipstick alone.

"The urine dipstick test may be an adequate stand-alone screen for UTI in febrile infants while awaiting urine culture results," the authors write.

The combined test performed better than dipstick testing alone in a sensitivity analysis (94.7% [95% CI, 94.4% - 95.0] vs 90.8% [95% CI, 90.4% - 91.2%]; P < .001). However, specificity for the dipstick test was higher than combined testing (93.8% [95% CI, 93.5% - 94.1%] vs 87.6% [95% CI, 87.2% - 88.0%]; P < .001). The specificity of dipstick testing was also better than microscopic analysis alone, which had a specificity of 91.3% (95% CI, 90.9% - 91.7%; P < .001 for the comparison).

Two coauthors have unrelated intellectual property interest and receive royalties from BioFire Diagnostic Inc. The other authors have disclosed no relevant financial relationships.

Pediatrics. Published online April 28, 2014. Abstract

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