In the present study we found that fibrinogen plasma concentrations were elevated both in patients with PAH and CTEPH compared to non-PH patients at risk. We could show that in CTEPH patients, but not in PAH patients, fibrinogen plasma concentrations were correlated with markers of disease severity, haemodynamics and CRP concentrations (as a surrogate marker for inflammation). Most importantly, fibrinogen plasma concentrations represent an independent predictor of impaired haemodynamics in CTEPH. Moreover, ROC analysis for detection of at-risk CTEPH patients showed a high specificity with a moderate sensitivity.