Electrolyte Imbalance in Infants Younger Than 90 Days of Age With Febrile Urinary Tract Infection

Aim To analyse the prevalence of electrolyte and kidney function alterations in infants ≤ 90 days with febrile urinary tract infection (UTI). Methods Secondary analysis of a prospective registry including infants ≤ 90 days with fever without a source seen between 2010 and 2022 in an emergency department. We analysed electrolyte and kidney function laboratory parameters in relation to the definitive diagnosis and a group of healthy controls. Results We registered 2361 episodes: 495 UTI (34 with an associated invasive bacterial infection [IBI]), 43 IBI not related to a UTI, and 1823 without bacterial infection. Further, we included 205 healthy controls. The median duration of fever was 4 h, and 98.5% were well appearing. Among infants with UTI without an associated IBI, blood creatinine levels were abnormal in 0.2%, urea in 1.1% and glomerular filtration rate in 3.2%, similar to infants not diagnosed with bacterial infections and healthy controls, and significantly lower than in those with UTI and an associated IBI (9.4%, 18.1% and 17.2% respectively). No patients had signs or symptoms of acute kidney injury. Conclusions Electrolyte imbalance and kidney function impairment are rare in well‐appearing infants younger than 90 days with febrile UTI and a short duration of fever.