In contrast to patients with traditional forms of pulmonary arterial hypertension (eg, idiopathic, scleroderma associated) who are symptomatic with mean pulmonary artery pressures (mPAPs) in the range of 50 to 60 mm Hg, patients with hemolytic disorders have a mild-to-moderate degree of elevation in mean pulmonary pressures (30-40 mm Hg), with mild elevations in pulmonary vascular resistance. These patients also have coexistent mild elevation in pulmonary capillary wedge pressure, suggesting left-sided heart failure (Table 1). Right-sided heart catheterization data show that the hemodynamic etiology of PH in these patients is multifactorial. In our cohort,16 pulmonary arterial hypertension (defined by an mPAP ≥ 25 mm Hg and a wedge pressure ≤ 15 mm Hg) was present in 54% of catheterized patients with SCD, whereas pulmonary venous hypertension secondary to left ventricular diastolic dysfunction (defined by an mPAP ≥ 25 mm Hg and a wedge pressure > 15 mm Hg) was present in 46%. If a more conservative definition is applied to classify these patients, pulmonary arterial hypertension (defined by an mPAP ≥ 25 mm Hg, pulmonary vascular resistance ≥ 160 dyne/s/cm5, and a wedge pressure ≤ 15 mm Hg) is present in 42%, pulmonary venous hypertension (defined by an mPAP ≥ 25 mm Hg and a wedge pressure > 15 mm Hg) is present in 46%, and PH secondary to a hyperdynamic state (defined by an mPAP ≥ 25 mm Hg, pulmonary vascular resistance < 160 dyne/s/cm5, and a wedge pressure ≤ 15 mm Hg) is present in 12% of catheterized patients (Fig 3). A recently presented study of a French cohort of patients with SCD revealed slightly different results but confirmed the multifactorial etiology of elevated pulmonary artery pressures in this population.53 The researchers reported that 6% of their screened cohort had an mPAP ≥ 25 mm Hg, even after excluding patients with chronic renal insufficiency, low total lung capacity, and evidence of liver dysfunction, which all are common complications of SCD. Of the patients with an mPAP ≥ 25 mm Hg, 55% had pulmonary venous hypertension, 22.5% had pulmonary arterial hypertension, and 22.5% had PH secondary to a hyperdynamic state.