Integrating Urinary Sodium into the Larissa Heart Failure Risk Score Improves Early Risk Stratification in Acute Heart Failure

(1) Introduction: Early identification of patients at high risk of recurrent events after hospitalization for acute decompensated heart failure (ADHF) remains challenging. The Larissa Heart Failure Risk Score (LHFRS) is a simple prognostic tool based on hypertension, coronary artery disease, and red blood cell distribution width. Urinary sodium has recently emerged as an objective marker of natriuretic response and decongestion. We prospectively evaluated whether incorporation of urinary sodium improves the prognostic performance of the LHFRS. (2) Methods: This prospective single-center observational study enrolled 130 consecutive adults hospitalized with ADHF. Clinical, laboratory, electrocardiographic, and echocardiographic data were collected at admission. Spot urinary sodium and chloride were measured at admission and 2 h after intravenous loop diuretic administration according to a standardized decongestion protocol. The primary endpoint was heart failure rehospitalization within 3 months. Secondary endpoints included all-cause mortality and the composite of death or heart failure rehospitalization. Multivariable logistic regression with bootstrap internal validation (1000 resamples) was used to identify independent predictors of outcomes. (3) Results: The study population included patients across the spectrum of heart failure phenotypes (HFrEF 58%, HFmrEF 7%, HFpEF 35%). During follow-up, 48 patients (36.9%) experienced heart failure rehospitalization and 23 (17.7%) died. The LHFRS independently predicted 3-month rehospitalization (B = 0.490, p = 0.041). Admission urinary sodium and 2-h urinary sodium provided incremental prognostic information beyond the LHFRS and remained independently associated with rehospitalization after multivariable adjustment (p = 0.008 and p = 0.001, respectively). Urinary chloride demonstrated similar prognostic associations, whereas conventional renal biomarkers, including serum creatinine, urea, estimated glomerular filtration rate, serum sodium, and NT-proBNP, did not consistently retain independent prognostic significance. The LHFRS was also significantly associated with the composite endpoint of death or rehospitalization (B = 1.173, p = 0.002), while its association with mortality alone was not statistically significant (B = −5.551, p = 0.256). (4) Conclusions: Lower admission and 2-h urinary sodium concentrations were associated with 3-month HF rehospitalization after adjustment for the LHFRS. These findings are hypothesis-generating and require confirmation in larger, externally validated multicenter cohorts.