As shown in Fig. 2a and b, patients with higher serum CXCL13 as defined by levels above the respective group medians did not have a higher mortality risk compared to their counterparts with lower serum CXCL13 (p = 0.786 for the IPAH cohort and p = 0.330 for the CTEPH cohort). Here, CXCL13 is linked to chronic thromboembolic pulmonary hypertension.