The plasmatic glycoprotein fibrinogen is both marker of inflammation and central player in the coagulation cascade9 characterised by its interaction with thrombin leading to conversion of fibrinogen to fibrin by limited proteolysis. Fibrin-stabilising-factor then causes cross-linkage of fibrin-molecules and consequently thrombus formation. Fibrinogen is induced by IL-6 as part of the acute phase reaction10. Interestingly, fibrinogen concentrations have recently been shown to be elevated in a small cohort of PAH patients11 and elevated fibrinogen plasma concentrations are considered as risk factor for coronary heart disease12. However, the diagnostic or predictive potential of fibrinogen has not yet been assessed in PH.