NPPB and myalgic encephalomeyelitis/chronic fatigue syndrome: The increased risk of mortality associated with worsening CFS scores was consistent across both subgroups: NT-proBNP >10,000 pg/L (HR: 2.6; 95% CI: 1.3-5.0; P < 0.001) and NT-proBNP <10,000 pg/L (HR: 4.4; 95% CI: 3.0-6.5; P < 0.001) (P for interaction = 0.58).