Final answer:
Paroxysmal nocturnal hemoglobinuria is characterized by intravascular hemolysis and thrombocytopenia, which is a reduction in the number of platelets in the bloodstream.
Step-by-step explanation:
Paroxysmal nocturnal hemoglobinuria (PNH) is primarily characterized by intravascular hemolysis, which is the destruction (lysis) of erythrocytes and the release of their hemoglobin into the circulation. Another characteristic associated with this condition is thrombocytopenia, which involves a lower-than-normal number of platelets in the blood. This increased tendency for blood clot formation (thrombosis) in PNH can lead to life-threatening complications such as deep vein thrombosis and pulmonary embolism, making thrombocytopenia a critical aspect of the disease.