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
Donath Landsteiner antibody is seen in- 
Select and explain. 
A. PNH, B. Waldenstrom's macroglobulinemia, C. Paroxysmal cold hemoglobinuria, D. Malaria
C: Paroxysmal cold hemoglobinuria
Answer: C: Paroxysmal cold hemoglobinuria 
Explanation: Paroxysmal cold hemoglobinuria (PCH)

PCH is characterized by intermittent massive intravascular hemolysis frequently with hemoglobinuria at low temperature.
The autoantibodies are of IgG class, also known as Donath-Landsteiner antibody.
These antibodies are directed against P-antigen on RBC.
Antigen-antibody complex on the red blood cell activates complement.
As a result, a large amount of membrane attack complex forms which destroys red cells directly → intravascular hemolysis.
Causes are: - Syphilis, Mycoplasma, Mumps, Measles, Flu syndrome