Lower cutoff optimizes UTI diagnosis in children undergoing bladder catheterization

September 14, 2023

3 min read

Source/Disclosures

Disclosures:
Sheikh reports no relevant financial disclosures. Please see the study for all other authors’ relevant financial disclosures. Eickhoff and Wald report no relevant financial disclosures.

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Key takeaways:

• Current guidelines endorse a cutoff of 50,000 colony-forming units per milliliter in urine to determine UTIs.
• A study found that a cutoff of 10,000 identified more UTIs in febrile children.

Data from a new study suggested a new standard cutoff for determining urinary tract infections in febrile children undergoing bladder catheterization, according to results published in Pediatrics.

According to Nader Shaikh, MD, MPH, professor of pediatrics and clinical and translational science at the University of Pittsburgh School of Medicine, no studies to date have compared a urine culture with a culture-independent reference standard, but current guidelines endorse a cutoff of 50,000 colony forming units (CFU)/mL.

“For the past 7 years or so, we’ve been using a definition for UTI that was based on a good guess,” Shaikh told Healio. “We wanted to look at the cutoff that’s used in a more scientific way, to figure out what was the best option for a cut off. … This is the first study to compare [this guess] with another standard to try to better understand how to diagnose the correct number of urinary tract infections.”

In their proof-of-concept study, Shaikh and colleagues evaluated the diagnostic properties of conventional urine culture at cutoffs of 10,000 CFU/mL, the standard 50,000 CFU/mL and 100,000 CFU/mL to identify UTI cases using 16S ribosomal RNA (rRNA) sequencing as the reference standard. Researchers considered a participant to have a UTI if at least 80% of sequences belonged to a single taxon and if they found evidence of a host inflammatory response in the urine.

The study included 341 children aged younger than 3 years (74% girls; 40% aged 2 to 11 months; 67% white) who underwent bladder catheterization, of which 64% had a documented temperature of at least 39°C. Among these children, there were 46 confirmed UTIs.

Using a cutoff of 10,000 CFU/mL identified 45 of the 46 UTIs (sensitivity of 98%; 95% CI, 93%-100%; specificity of 99%; 95% CI, 97%-100%). A cutoff of 50,000 CFU/mL demonstrated a sensitivity of only 80% (95% CI, 68%-93%) in identifying only 37 cases and had a “negligible effect” on specificity compared with the lower cutoff, according to the researchers. Using a cutoff of 100,000 CFU/mL showed a greater drop in sensitivity to 70% (95% CI, 55%-84%), but again, showed similar specificity.

“This diagnostic accuracy study provides support for the use of a cutoff of 10,000 CFU/mL to diagnose UTI in febrile children undergoing bladder catheterization,” Shaikh said in a video abstract included with the study online.

Shaikh said an additional concern is the “overuse of antibiotics” associated with UTIs.

“In this case, using a lower cutoff did not reduce the specificity of the urine culture,” Shaikh said. “If we lower the cutoffs, we won’t be diagnosing more kids without urinary tract infection. It doesn’t cause inappropriate use of antibiotics.”

“This study told us that we’ve been underdiagnosing UTIs for quite a long time,” he said.

The study was accompanied by an editorial authored by Jens C. Eickhoff, PhD, and Ellen R. Wald, MD, both of the School of Medicine and Public Health at University of Wisconsin-Madison.

“One advantage of 16S sequencing over conventional culture is that it can indicate the presence of organisms difficult to culture conventionally,” Eickhoff and Wald wrote. “There is also the exciting future promise of rapid turnaround times for 16S sequencing and the potential for determining the presence of antibiotic-resistant organisms. This method could provide a more comprehensive picture of the microorganisms in urine than is possible with culture.”

The challenge in the future would not only be determining what is in urine, but “judging whether it reflects infection or contamination,” the authors added.

“The results of this study affirm the strength of current culture techniques, provide a step forward in helping to capture important symptomatic UTIs that may occur with low colony counts (a threshold of 10,000 CFU/mL is reasonable) but with evidence of urinary inflammation, and endorse continued exploration of 16S rRNA sequencing as a diagnostic aid in UTI,” Eickhoff and Wald wrote.

Reference:

Wald ER, et al. Pediatrics. 2023;doi:10.1542/peds.2023-062883.

Shaikh N, et al. Pediatrics. 2023;doi:10.1542/peds.2023-061931.

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