Blood analysis for screening of electrolyte and kidney function alterations in patients with febrile urinary tract infection.

Aim: To describe the prevalence, severity, risk factors, and clinical relevance of electrolyte disturbances and acute kidney injury (AKI) during febrile urinary tract infection (fUTI).

Methods: Retrospective observational study of well/fair-appearing patients between 2 months and 16 years, with no previous relevant medical history, diagnosed with fUTI in the paediatric emergency department (PED) with subsequent microbiological confirmation. Analytical alteration (AA) data were considered: AKI (creatinine elevation × 1.5 the median for age), plasma sodium alteration (≤130 or ≥150 mEq/L), and potassium alteration (≤3 or ≥6 mEq/L).

Results: We included 590 patients, 17.8% presented AA (13 hyponatremia, 7 hyperkalaemia, and 87 AKI). No patient presented severe analytic alterations or a higher frequency of symptoms potentially attributable to these alterations (seizures, irritability, or lethargy). Risk factors associated with these AA were clinical dehydration (OR = 3.5 95% CI: 1.04-11.7; p = 0.044) and presenting a temperature >39°C (OR = 1.9 95% CI: 1.14-3.1; p = 0.013).

Conclusions: Electrolyte and renal function disturbances are infrequent in the previously healthy paediatric population with a fUTI. If present, they are asymptomatic and not severe. Based on our results, performing systematic blood analysis to rule out AA appears no longer justified, especially in the absence of risk factors.