Group 1.4.6 Chronic hemolytic anemia 
The chronic hemolytic anemias represent a subcategory of PAH. There has been increasing evidence that PAH is a complication of chronic hereditary and acquired hemolytic anemias, including sickle cell disease [46,47], thalassemia [48], hereditary spherocytosis [49], stomatocytosis [50], and microangiopathic hemolytic anemia [51].
PH has been reported most frequently in patients with sickle cell disease, however the prevalence of PAH is not yet clearly established. The prevalence of PH in sickle cell disease is undoubtedly much lower than 32% as suggested by echocardiography [47]. Recently, a prospective epidemiologic studies using echocardiographic screening and direct hemodynamic confirmation were conducted in 398 outpatients with sickle cell disease at referral centers in France [52]. In this study, the prevalence of a tricuspid regurgitant jet velocity of at least 2.5 m per second measured by echocardiography was 27%. In contrast, the prevalence of pulmonary hypertension confirmed on catheterization was only 6%, suggesting that echocardiographic evaluation alone had a low positive predictive value for PH in this population. Indeed, the precise mechanism of PAH in sickle cell disease remains uncertain.