What is the hallmark feature of hemolysis seen in PNH?

Paroxysmal nocturnal hemoglobinuria (PNH) is a disorder characterized by the destruction of red blood cells due to a deficiency of certain proteins that protect them from being attacked by the body's immune system. The hallmark feature of hemolysis in PNH is indeed recurrent, episodic intravascular hemolysis. This means that hemolysis can occur suddenly and unpredictably, often leading to symptoms such as dark urine, fatigue, and abdominal pain during episodes.

In PNH, the red blood cells are particularly vulnerable to lysis by complement activation, especially at night when the body is in a more acidic state. This results in intravascular hemolysis as red blood cells burst within the bloodstream. The episodic nature reflects how hemolytic episodes can be triggered by various factors such as infections, stress, or underlying health conditions.

The other options highlight aspects of hemolysis or anemia but do not capture the specific periodic nature of hemolysis that is characteristic of PNH. Chronic extravascular hemolysis typically involves the spleen and is not the main feature of PNH. Similarly, while normocytic anemia can occur as a result of hemolysis, it does not encapsulate the episodic