NPPB and heart failure: Here, we found strong associations between GDF-15 levels and established markers of renal dysfunction (e.g., creatinine (r = 0.481, p < 0.001) and cystatin C (r = 0.553, p < 0.001)), cholestasis (e.g., bilirubin (r = 0.195, p = 0.004) and γGT (r = 0.200, p = 0.003)), impaired hepatic synthesis (e.g., albumin (r = −0.206, p = 0.028), PCHE (r = −0.149, p = 0.037), and prothrombin time (r = −0.314, p < 0.001)), and cardiac failure (e.g., brain natriuretic peptide (r = 0.278, p = 0.024)).