Urinary sodium, baseline loop diuretic dose, and short-term outcomes in ambulatory worsening heart failure: The NaU/F Index

Background Worsening heart failure (WHF) carries high short-term morbidity and mortality. Spot urinary sodium (NaU) is increasingly used to assess diuretic response but does not account for chronic loop diuretic exposure.Objectives To determine whether a urinary sodium-to-furosemide index (NaU/F) improves short-term risk stratification compared with isolated NaU in ambulatory WHF METHODS: Retrospective analysis of a prospective cohort of consecutive adults treated in a specialized heart failure day-hospital program (August 2023-April 2025). Spot NaU was measured 2 hours after intravenous loop diuretic administration. NaU/F was calculated as urinary sodium divided by baseline oral furosemide dose (40-mg equivalents).Primary endpoint 30-day composite of HF rehospitalization, unplanned outpatient visit, or all-cause mortality.Results 130 patients were included (mean age 77.8 ± 10.8 years; 74.6% male; LVEF 42.2 ± 18.2%). The primary endpoint occurred in 10.9%. NaU Conclusion In ambulatory WHF, NaU/F outperformed isolated urinary sodium for short-term risk stratification. Contextualizing natriuretic response to chronic loop diuretic exposure may refine prognostic assessment and warrants prospective validation.