To the Editor,
We thank Park and Shin for their thoughtful comments [1] regarding our recent article on electrolyte imbalance and kidney function impairment in infants younger than 90 days with febrile urinary tract infection (UTI) [2].
We agree with the authors that hyponatraemia may reflect a higher inflammatory burden in children with febrile UTI. Indeed, their previous work demonstrated an association between hyponatraemia, inflammatory markers and renal cortical defects identified by DMSA scintigraphy [3]. In our cohort, hyponatraemia was also the most frequent electrolyte abnormality, being detected in 36.5% of infants with UTI [2].
However, it is important to emphasise that most cases in our study were mild, with moderate‐to‐severe hyponatraemia (< 130 mEq/L) observed in only 1% of patients [2]. Furthermore, hyponatraemia was also identified among nearly 25% of infants with nonbacterial infections, suggesting that systemic inflammatory response itself may contribute substantially to this finding, beyond the specific diagnosis of UTI. On the other hand, our sample included young febrile infants brought very early to the ED (in the manuscript by Park et al. [3], children with renal cortical defects diagnosed after DMSA scintigraphy the duration of fever was significantly longer) and UTI diagnosis required positive urine culture together with abnormal urine dipstick test results.
We also appreciate the discussion regarding hyperkalaemia and the possibility of secondary pseudohypoaldosteronism. This is an interesting hypothesis, particularly in young infants with pyelonephritis or invasive bacterial infection. Previous studies have described transient pseudohypoaldosteronism associated with febrile UTI and electrolyte abnormalities in infants [4]. Nevertheless, several aspects of our results suggest that at least part of the observed hyperkalaemia may have been artifactual. First, hyperkalaemia was unexpectedly more frequent among healthy controls than among infants with UTI [2]. Second, none of the infants showed clinical manifestations attributable to potassium imbalance, and no electrolyte abnormality required specific therapeutic intervention. Finally, obtaining non‐haemolysed blood samples in very young infants is often technically challenging in routine clinical practice.
Importantly, our study population consisted predominantly of well‐appearing infants with a short duration of fever before presentation [2]. In this context, the overall prevalence of clinically significant electrolyte or kidney function abnormalities was very low. We therefore believe that our findings support the idea that routine detection of mild electrolyte abnormalities should be interpreted cautiously and within the broader clinical context.
We fully agree that further prospective studies are needed to clarify the pathophysiological mechanisms underlying electrolyte disturbances in febrile infants with UTI and to determine whether these abnormalities may help identify patients at increased risk of invasive bacterial infection or renal involvement.
Author Contributions
M. Serrano Oarbeaskoa: conceptualization, supervision. M. Camarero Pagonabarraga: supervision. I. Iriarte Uribeecheverria: supervision. I. Gangoiti: supervision. B. Gomez: supervision. D. Jimenez‐Gonzalez: supervision. S. Mintegi: conceptualization, supervision.
Linked Articles
Electrolyte Imbalance in Infants Younger Than 90 Days of Age With Febrile Urinary Tract Infection. https://doi.org/10.1111/apa.70291.
Electrolyte Imbalance in Young Infants with Febrile UTI: Is it a Marker of Severity? https://doi.org/10.1111/apa.70644.
Data Availability Statement
The data that support the findings of this study are available from the corresponding author upon reasonable request.
References
- 1. Park S. J. and Shin J. I., “Electrolyte Imbalance in Young Infants With Febrile UTI: Is It a Marker of Severity?,” Acta Paediatrica 115, no. 9 (2026): 2046–2047, 10.1111/apa.70644. [DOI] [PubMed] [Google Scholar]
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The data that support the findings of this study are available from the corresponding author upon reasonable request.