Patients with hemolytic disorders (e.g. sickle cell anemia or thalassemia) are known to develop pulmonary hypertension. Hemolysis is where red blood cells are destroyed and their contents released into the circulation. It is thought that these red-cell contents cause constriction and thrombosis of the blood vessels in the lungs. Conversely, it is possible that patients with pulmonary hypertension have hemolysis.