Thrombocytopenia Independently Predicts Death in Idiopathic PAH

Background: Pulmonary arterial hypertension (PAH) is a progressive vascular disorder with a high mortality. Clinical experience and small case series suggest thrombocytopenia may be frequent in this population and associated with a poor prognosis. We sought to estimate the prevalence of thrombocytopenia in patients with PAH and characterize its association with disease characteristics and patient outcome.

Methods: Single center cohort study of 714 incident adult patients with Group 1 PH who were evaluated for baseline platelet count at the time of diagnosis. Pts were stratified into three groups: normal platelet count (>150 × 10/L), Grade 1 thrombocytopenia (75-149 × 10/L) and Grade 2-4 thrombocytopenia (<75 × 10/L).

Results: The median platelet count was 209 × 10/L (IQR 163, 264). There were 572 (80%) pts without thrombocytopenia, 107 (15%) with Grade 1 and 35 (5%) with Grade 2-4 thrombocytopenia. The median pt age was 55 years (IQR 44-65) with no difference between platelet groups (p = 0.85). Men were more likely to have thrombocytopenia (62, 34%) than women (80, 15%, p < 0.0001). Thrombocytopenia was frequent with portopulmonary PAH (84%) as opposed to idiopathic PAH (iPAH; 14%) or connective tissue disease associated PAH (12%). Platelet counts were not associated with functional class symptoms, the degree of right ventricular enlargement or dysfunction or tricuspid regurgitation by echocardiography. Invasive hemodynamics of right atrial pressure, mean pulmonary artery pressure and pulmonary vascular resistance were also similar between platelet groups. Thrombocytopenia was associated with higher mortality in iPAH patients (age- and sex-adjusted 5 year mortality [HR 1.95 (1.20, 3.08) p = 0.008] but not in other etiology groups. In a multivariate model of iPAH patients (adjusted for age, sex, DLCO, PVR, creatinine and 6MW distance) thrombocytopenia was most predictive of 5-year mortality [HR 1.68 (1.32, 2.12), p < 0.0001].

Conclusion: Thrombocytopenia in the context of iPAH portends a poor prognosis and is a simple independent factor to consider in judging severity of disease.