This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
Intravascular hemolysis occurs in: 
Select and explain. 
A. Hereditary spherocytosis, B. Autoimmune haemolytic anemia, C. Paroxysmal nocturnal hemoglobinuria, D. Thalassemia
C: Paroxysmal nocturnal hemoglobinuria
Answer: C: Paroxysmal nocturnal hemoglobinuria 
Explanation: PNH is a disease that results from acquired mutations in the phosphatidylinositol glycan complementation group A gene (PIGA), an enzyme that is essential for the synthesis of certain cell surface proteins.
Red cells, platelets, and granulocytes deficient in these GPI-linked factors are abnormally susceptible to lysis by complement. In red cells, this manifests as intravascular hemolysis, caused by the C5b-C9 membrane attack complex.

 

The triad of hemolysis, pancytopenia and thrombosis is unique to PNH.
Thrombosis is the leading cause of disease-related death in PNH.
PNH is best made with flow cytometry in which there is presence of bimodal distribution of the red cells.