Pyuria is an important tool in diagnosing UTI in infants

In this issue of Pediatrics, Chaudhari et al. share the results of a study of the impact of urine concentration on the optimal threshold in the new era of automated urinalysis. Centrifugation of urine specimens has long been standard laboratory practice, presumably performed to concentrate sediment and facilitate the detection of cellular elements and bacteria.

However, for the many sites that do not have machines for automated urinalyses (virtually all office practices, for example), the most important finding in this study may well be how well LE [leukocyte esterase] performs regardless of urine concentration. The optimal threshold for LE is not clear, however. The authors use “small” as their threshold for LE. At any threshold, can a negative urinalysis be relied on to exclude the diagnosis of UTI? A “positive” culture without inflammation evident in the urine is likely due to contamination, very early infection (rare), or asymptomatic bacteriuria (positive urine cultures in febrile children can still represent asymptomatic bacteriuria, because the fever may be due to a source other than the urinary tract).

If there are, in fact, some true UTIs without evidence of inflammation from the urinalysis, are they as harmful as those with “pyuria”?

Animal data demonstrate it is the inflammatory response, not the presence of organisms, that causes renal damage in the form of scarring. So the role of using evidence of inflammation in the urine to screen for who needs a culture seems justified on the basis not only of practicality at point of care and likelihood of UTI, but also sparing individuals at low to no risk of scarring from invasive urine collection. Moreover, using the urinalysis as a screen permits selecting individuals for antimicrobial treatment 24 hours sooner than if clinicians were to wait for culture results before treating. The urinalysis provides a practical window for clinicians to render prompt treatment. And Chaudhari et al. provide valuable assistance for interpreting the results of automated urinalyses.

Kenneth B. Roberts, MD , is a professor of therapeutic radiology at Yale University, New Haven, Conn. He did not report any relevant financial disclosures. These comments are excerpted from a commentary that accompanied Dr. Chaudhari and his associates’ study ( Pediatrics. 2016;138(5):e20162877 ).