Importantly, survival analysis showed that high levels of KP-metabolites (Kyn, 3-HK, QA, 3-HA, and KA) were strongly associated with worse mortality even after adjusting for age, sex, PAH type (iPAH or APAH) and PAH therapy type (no therapy or mono or double or triple therapy). Here, NPPA is linked to pulmonary arterial hypertension.