fibrinQ. Can you help me understand intrinsic vs. extrinsic anemias? My concept of it is that intrinsic means it’s in the blood vessels and extrinsic means it’s in the spleen. Is this a correct assumption? Or not necessarily?

A. Usually, when we use the words intrinsic and extrinsic in reference to anemias, we’re talking about the things that cause hemolytic anemias. Some hemolytic anemias are caused by things intrinsic to the red cell itself (like a problem with the red cell membrane, as is the case in hereditary spherocytosis, or a problem with a red cell enzyme, as is the case in G6PD deficiency) vs. things that are extrinsic to the red cell (like the fibrin strands that rip apart red cells in microangiopathic hemolytic anemia).

I think the concepts you are referring to are intravascular hemolysis (which is hemolysis that happens in blood vessels, often due to complement activation) and extravascular hemolysis (which is hemolysis that happens in the spleen, often due to antibodies coating the red cells).