EDN1 and pulmonary arterial hypertension: It can be considered a low-quality biomarker in PAH for several reasons; firstly, it is not widespread; secondly, the clinical use of ET-1 in PAH diagnosis is limited by ET-1 very short half-life (about 5 min) [27]; in addition, the ET-1 plasma levels do not accurately represent the concentration of ET-1 in tissue [22] and are affected by several confounding factors, displaying ethnic (e.g., ET-1 levels are higher in people of African ethnicity), gender (i.e., ET-1 levels are higher in males), and age (i.e., ET-1 levels are higher with ageing) differences [28].