Rethinking Urine Culture Cutoffs for UTI Diagnosis in Young Children

Urinary tract infections (UTIs) in young children can be challenging to diagnose accurately. Conventionally, urine culture has been the go-to method, but it primarily favors the growth of specific organisms under aerobic conditions. Recent advancements in diagnostic techniques, such as 16S ribosomal ribonucleic acid (rRNA) gene amplicon sequencing, have given us a more unbiased view of the organisms present in urine. This breakthrough prompts us to reconsider the cutoff values used in urine culture to define a positive UTI in young children.

In a study conducted by Shaikh et al., the researchers employed 16S rRNA gene amplicon sequencing as the reference standard and calculated the accuracy of urine culture at various cutoff points. They classified children as having a UTI if they exhibited an elevated urinary marker of inflammation and had a relative abundance of ≥80% of any organism in the 16S rRNA gene amplicon sequencing.

The results unveiled an interesting trend. When the traditional cutoff of 10,000 colony-forming units per mL (CFU/mL) was applied, urine culture showed an impressive 98% sensitivity and 99% specificity. However, increasing the cutoff to 50,000 CFU/mL dropped the sensitivity to 80% without significantly altering the specificity. Further elevating the cutoff to 100,000 CFU/mL led to a sensitivity of 70%.

These findings indicate that conventional urine culture remains a reliable method for diagnosing UTIs in young children. Nonetheless, they also suggest that a cutoff of 10,000 CFU/mL for children undergoing bladder catheterization hits the ideal balance between sensitivity and specificity. This insight is invaluable in clinical practice as it allows for more accurate and efficient UTI diagnoses, helping to ensure timely treatment and better outcomes for young patients.

In conclusion, the study by Shaikh et al. challenges us to reassess the conventional cutoff values for urine culture in young children with suspected UTIs. By considering the optimal threshold of 10,000 CFU/mL, we can enhance our diagnostic accuracy and make more informed decisions in managing UTIs in this vulnerable population.

Shaikh N et al. Support for the Use of a New Cutoff to Define a Positive Urine Culture in Young Children. Pediatrics (2023) 152 (4): e2023061931. https://doi.org/10.1542/peds.2023-061931