Rethinking Ultrasound After a Child’s First Urinary Tract Infection: Radiologists Answer Their Critics

When a young child arrives at the emergency department with a febrile urinary tract infection, one of the most contested questions in pediatric imaging begins: should the child’s kidneys and bladder be examined with ultrasound, and if so, when? For decades, routine ultrasonography after a first urinary tract infection has been a cornerstone of pediatric practice, yet its diagnostic yield has been repeatedly questioned. A recent exchange published in Pediatric Radiology, in which radiologists from Ljubljana University Medical Centre respond to a critique of their work, has brought this long-running debate back into sharp focus, and the conversation touches on one of the most consequential trade-offs in modern medicine: how to balance the benefits of early detection against the costs and risks of over-imaging.

The exchange centers on a Matters Arising letter authored by Tjaš Žvar, Peter Slak, and Domen Plut, radiologists affiliated with both the Department of Radiology at Ljubljana University Medical Centre and the Faculty of Medicine at the University of Ljubljana. Their reply, published on 8 September 2026, responds to a commentary by Surve and Shitole concerning the optimization of imaging strategies after a first pediatric urinary tract infection. The tone of the reply is notably collegial. The Slovenian team thanks their colleagues for their insightful comments and frames the critique as a contribution that advances the discussion, but beneath the courteous surface lies a substantive disagreement about what the evidence currently supports and where pediatric imaging practice should go next.

At the heart of the discussion is a category of conditions known as congenital anomalies of the kidney and urinary tract, abbreviated CAKUT. These anomalies, which range from structural malformations of the kidney to obstructions and abnormal reflux of urine from the bladder back up the ureters, are among the most common abnormalities detected in children, and clinically significant forms can predispose a child to recurrent infections, hypertension, and progressive renal scarring. The clinical stakes are real. The goal of imaging after a first infection is to identify the subset of children whose anatomy puts them at risk of future kidney damage, so that surveillance, prophylaxis, or surgical correction can be considered before irreversible harm occurs.

The problem, as the Ljubljana authors acknowledge candidly, is that the current approach to identifying children with clinically significant CAKUT is not ideal. Routine ultrasonography after a first urinary tract infection has a low diagnostic yield, meaning that the vast majority of scans performed reveal nothing that changes management. This inefficiency carries costs that extend beyond the price of the examination itself. Every ultrasound appointment represents a burden on families, an addition to already stretched radiology departments, and, in some health systems, a delay that pushes other patients further down the waiting list. It was precisely this inefficiency, the authors write, that served as one of the principal motivations for their original study.

Crucially, the Slovenian team is careful to clarify the intent behind their work. Their aim, they explain, was not simply to reduce imaging, but to explore whether it could be more selectively targeted while maintaining patient safety. This distinction matters. Proposals to scale back imaging after a first urinary tract infection have sometimes been met with concern that children with hidden, clinically significant anomalies would be missed, with potentially serious consequences for their kidneys. By emphasizing that safety was a guiding constraint rather than an afterthought, the authors position their work as an attempt at refinement rather than retrenchment. They believe their findings point in the right direction, though they are equally forthright that further optimization is needed, because even within the higher-risk groups their study proposed, the diagnostic yield remains low.

This admission is one of the most scientifically interesting elements of the reply. It reflects a mature understanding of the limits of risk stratification in this field. The traditional predictors used to decide which children warrant imaging after a first infection have been relatively blunt instruments, principally age and sex, with atypical or recurrent infections triggering more aggressive workups. The authors concede that these variables alone do not capture the full spectrum of risk, and that even a risk-informed pathway built on them will leave a low yield within its targeted groups. In other words, refining the filter helps, but the filter itself may need to be rebuilt from richer material.

The reply to Surve and Shitole also engages with evidence from outside the immediate debate, drawing on a study by Doğan and colleagues that examined children diagnosed with vesicoureteral reflux, or VUR, only after they had already suffered recurrent infections. That study reported that children diagnosed with VUR following recurrent urinary tract infections had a higher prevalence of high-grade reflux and renal scarring. The implication is sobering: children whose significant urinary tract anatomy goes undetected after their first infection may return later with recurrent disease and already-established kidney damage. For the Ljubljana authors, this underscores the importance of identifying these children earlier, and it explains why they resist any interpretation of their work as a simple call for less imaging. The cost of missing a child with high-grade reflux is measured in permanent renal scarring, a price that no efficiency gain can justify.

So what would a better approach look like? The authors offer a concrete research agenda rather than a finished protocol. They argue that future studies should specifically examine children in whom clinically significant CAKUT or VUR was diagnosed only after the initial urinary tract infection, that is, the very patients whose anomalies were missed or not yet manifest at first presentation. By retrospectively analyzing these children’s initial clinical, microbiological, laboratory, and ultrasound findings together with their subsequent clinical course, researchers may uncover predictors that are not captured by age and sex alone. Such predictors could include specific patterns of organism virulence, inflammatory marker profiles, or subtle ultrasound findings that currently escape routine interpretation. The proposal effectively treats the missed cases as a natural experiment, a cohort whose histories hold the clues to earlier detection.

This methodology has a certain elegance, but it also illustrates the challenges inherent in the field. Retrospective analyses depend on the quality and completeness of the original records, and ultrasound findings in particular are operator-dependent and variably documented. Moreover, the number of children who experience clinically significant missed or delayed diagnoses after a first infection is small relative to the total population of children presenting with febrile urinary tract infections, which means that multi-center collaboration and careful pooling of data are likely to be essential. The authors’ call is therefore best understood as an invitation to the international pediatric radiology and urology communities to build the evidence base collaboratively, rather than as a claim that the answer is already at hand.

What emerges from this exchange is a picture of a specialty genuinely wrestling with its own practices in public. The original study, the critique by Surve and Shitole, and the reply from Žvar, Slak, and Plut together form a small but instructive case study in how scientific self-correction is supposed to work: findings are published, challenged, defended, and refined, with each participant acknowledging the limits of the current evidence. For clinicians, the practical message of the moment is one of continuity with caution. Risk-informed imaging pathways are, as the authors put it, a logical direction for future development, but the diagnostic yield remains low even within proposed higher-risk groups, and the consequences of delayed diagnosis of vesicoureteral reflux and renal scarring are serious enough that no wholesale abandonment of post-infection imaging is currently warranted. For families, the takeaway is that the ultrasound after a child’s first urinary tract infection remains a decision grounded in an active, evolving scientific debate, one in which researchers on all sides share the same goal: finding the children who need help, as early as possible, while sparing everyone else an unnecessary test.

Subject of Research: Risk-informed ultrasound imaging after a first pediatric urinary tract infection to detect congenital anomalies of the kidney and urinary tract

Article Title: Reply to Surve K

Article References: Žvar, T., Slak, P., & Plut, D. (2026). Reply to Surve K. Pediatric Radiology. https://doi.org/10.1007/s00247-026-06776-y

Image Credits: AI Generated

DOI: 10.1007/s00247-026-06776-y

Keywords: pediatric radiology, urinary tract infection, CAKUT, vesicoureteral reflux, ultrasound, renal scarring, risk stratification, diagnostic yield, children, imaging guidelines, nephrology, urology