Abstract:

Objective To investigate the incidence and associated risk factors of Na⁺/K⁺ imbalance in children with febrile urinary tract infection (FUTI). Methods A total of 716 children with FUTI hospitalized at Tianjin Children’s Hospital from January 2022 to December 2025 were included, and their clinical data were retrospectively analyzed. Na⁺/K⁺ imbalance was classified as hyponatremia (serum sodium <135 mmol/L), hypernatremia (serum sodium >145 mmol/L), hypokalemia (serum potassium <3.5 mmol/L), hyperkalemia (serum potassium >5.5 mmol/L), and hyponatremia with hyperkalemia (serum sodium <135 mmol/L accompanied by serum potassium >5.5 mmol/L). The incidence of each type of Na⁺/K⁺ imbalance was calculated. Logistic regression was used to identify factors associated with hyponatremia, hyperkalemia, and hyponatremia with hyperkalemia. Results Among the 716 included children, 305 cases (42.6%) had hyponatremia, 55 cases (7.7%) had hyperkalemia, 12 cases (1.7%) had hypokalemia, and no cases of hypernatremia were observed. In addition, 17 cases (2.4%) had hyponatremia with hyperkalemia. In multivariable logistic regression analysis, fever duration after antibiotic treatment and CRP were both independent risk factors for hyponatremia in children with FUTI (OR=1.361, 1.007; 95%CI: 1.203-1.540, 1.004-1.010; both P<0.01). Age and congenital anomalies of the kidney and urinary tract (CAKUT) were both independent risk factors for hyperkalemia in children with FUTI (OR=0.918, 2.574; 95%CI: 0.862-0.978, 1.409-4.701; P=0.008, 0.002). CRP and CAKUT were both independent risk factors for hyponatremia with hyperkalemia in children with FUTI (OR=1.011, 3.445; 95%CI: 1.004-1.018, 1.279-9.282; P=0.002, 0.014). Even after adjusting for renal hypoplasia, pelvicalyceal dilatation, ureteral dilatation, and non-Escherichia coli infection, CAKUT remained an independent risk factor for hyponatremia with hyperkalemia in children with FUTI (OR=8.098, 95%CI: 2.196-29.863, P=0.002). Conclusion Among children with FUTI, Na⁺/K⁺ imbalance most commonly manifests as hyponatremia, followed by hyperkalemia and hyponatremia with hyperkalemia. During the course of pediatric FUTI, hyponatremia may indicate a more severe inflammatory response, and children with concomitant hyperkalemia should be evaluated for possible underlying CAKUT.

Key words: urinary tract infection, children, secondary pseudohypoaldosteronism, sodium, potassium