Blood gas analysis is normal in the early stages, later pO2 is reduced, pCO2 increased, later reduced and HCO3 increased. The red blood count in advanced stages of PH secondary to congenital heart disease or hypoxaemia presents polycythaemia and haematocrit > 50%. In cases of iPAH, both atrial natriuretic peptide (ANP) and “brain natriuretic peptide” (BNP) correlate with survival, and BNP and NT-BNP are independent predictors of mortality . Increased uric acid (resulting from compromised oxidative metabolism) and increased troponin T levels (resulting from right ventricular ischaemia) correlate with a poor prognosis  . At present, proBNP levels are the most commonly used biomarkers. They correlate with enlargement, compressive stress and reduced function of the right ventricle.