Challenging and perplexing case of hemolytic anemia today! Two entities that were discussed are highlighted below:
Paroxysmal Nocturnal Hemoglobinuria (PNH)
- Rare! 1-10 cases per per million people
- Caused by an abnormality of the GPI anchoring protein that protects the RBCs from complement
- Test for CD55 and CD59 with flow cytometry
- Classic presentation is unexplained hemolytic anemia, but can be associated with aplastic anemia and can have increased risk of thrombosis (hypercoagulable due to free Hgb in blood or other mechanisms?).
- This is usually an acquired condition
- Turns out that hemolysis can occur throughout the day and not just at night. Often there can be triggers causing hemolysis.
- Think about PNH when you have a patient with a hemolytic anemia that is DAT negative
Paroxysmal Cold Hemoglobinuria (PCH)
- Caused by an IgG Ab that fixes complement in the cold, but only causes intravascular hemolysis upon rewarming
- Classic presentation is hemoglobinuria occurring after patient exposure to cold
- DAT should be positive for complement and negative for IgG
- There is also a separate but similar entity of autoimmune hemolytic anemia due to IgM cold agglutinins. This is often triggered by infection or underlying lymphoproliferative disorder and can also cause intravascular hemolysis. Watch out for hyperviscosity with IgM!