Estimation of salt intake from urinalysis as a prognostic indicator in patients with heart failure

Abstract Background Restricting sodium consumption by reducing salt intake is crucial in heart failure management. The average salt intake in Japan is approximately 10 g/day, which is significantly higher than that in other countries. Therefore, the Japanese guidelines for heart failure recommend a target salt intake of less than 6 g/day. Purpose Excessive salt intake is a well-known risk factor for heart failure, but it has also been reported that excessive salt restriction does not affect clinical outcomes in patients with heart failure. Moreover, although previous reports have mainly focused on clinically stable patients with chronic heart failure, appropriate salt intake management in patients with unstable heart failure immediately after hospital discharge remains unexplored. Therefore, this study aimed to investigate the effect of salt intake management on patients with heart failure in the early post-discharge period. Methods The study was conducted between April 2015 and March 2023, and included 395 of 4,292 patients (mean age: 72 y; sex: 63% male) who were hospitalized owing to heart failure and whose salt intake was measured at early post-discharge. Salt intake was estimated via the Tanaka Method, using spot urine samples. The patients were divided into four groups based on the estimated salt intake: very low (< 4 g/day) (n = 24), low (≥ 4 and < 7 g/day) (n = 109), high (≥ 7 and < 10 g/day) (n = 149), and very high (≥ 10 g/day) (n = 113). The primary endpoint was all-cause rehospitalization within 1 year of discharge. Results During a median follow-up period of 303 days, 153 rehospitalization occurred. 96 were heart failure rehospitalization; others included infection, arrhythmia, dehydration etc. Spline curve analysis for estimated salt intake and rehospitalization (Fig. 1) showed a significant nonlinear curve (P = 0.017). Cox regression analysis (Fig. 2) revealed a significantly higher number of rehospitalization in the very low group (hazard ratio [HR]: 2.29; 95% confidence interval [CI]: 1.24–4.25; P = 0.009), compared with the low group, and a similar trend was also observed in the very high group (HR: 1.51; 95% CI: 0.99–2.31; P = 0.056). Subgroup analysis (Fig. 3) showed that the impact of estimated salt intake on rehospitalization, as represented by a U-shaped curve, was more pronounced in patients who were not treated with loop or thiazide diuretics. Conclusion The results of this study suggest that both excessive salt intake and excessive restriction may increase the risk of rehospitalization in patients with heart failure during the early post-discharge period. Additionally, the results indicate that estimation of salt intake using the Tanaka method may be particularly useful for patients not undergoing diuretic treatment. Conversely, patients with very low salt intake, potentially indicative of inadequate oral intake due to an impaired general condition, may require careful follow-up.