Impact of Serum Indoxyl Sulfate on One-Year Adverse Events in Chronic Kidney Disease Patients with Heart Failure

Background/Objectives: Indoxyl sulfate, a uremic toxin, is associated with mortality and cardiovascular events in patients with chronic kidney disease (CKD). This study aimed to evaluate the prognostic implications of serum indoxyl sulfate levels in patients with heart failure and CKD. Methods and Results: This was a prospective multicenter observational study. Overall, 300 patients with chronic heart failure with a previous history of hospitalization and an estimated glomerular filtration rate (eGFR) of 45 mL/min/1.73 m² or less (CKD stage G3b to G5) without dialysis were analyzed. The primary outcome assessed in a time-to-event analysis from the measurement of indoxyl sulfate was a composite of all-cause death, hospitalization for heart failure, nonfatal myocardial infarction, and nonfatal stroke. Clinical events were followed-up to one year after indoxyl sulfate measurement. The median patient age was 75 years, and 57% of the patients were men. We divided the cohort into low and high indoxyl sulfate categories according to a median value of 9.63 mg/mL. The primary outcome occurred in 27 of 150 patients (18.0%) in the low indoxyl sulfate group and 27 of 150 patients (18.0%) in the high indoxyl sulfate group (hazard ratio, 1.00; 95% confidence interval, 0.58 to 1.70, p = 0.99). In the post hoc exploratory analyses, the results were consistent across age, sex, body mass index, left ventricular ejection fraction, eGFR, and N-terminal pro b-type natriuretic peptide. Conclusions: Among heart failure patients with CKD stages G3b to 5G, serum indoxyl sulfate concentrations were not significantly associated with the subsequent occurrence of cardiovascular events.