A syndrome marked by exaggerated splenic activity and, possibly, splenomegaly, hypersplenism causes peripheral blood cell deficiency as the spleen traps and destroys these cells.

In this disorder, the spleen’s normal filtering and phagocytic functions accelerate indiscriminately, automatically removing antibody–coated, aging, and abnormal cells, even though some cells may be functionally normal. The spleen may also temporarily sequester normal platelets and red blood cells (RBCs), withholding them from circulation. In this manner, the enlarged spleen may trap as much as 90% of the body’s platelets and up to 45% of its RBC mass.