Intravascular hemolysis occurs in:
Hereditary spherocytosis
Autoimmune haemolytic anemia
Paroxysmal nocturnal hemoglobinuria
Thalassemia
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.