Asplenia: The absence of a spleen or one that functions. (The spleen can be functionally destroyed, as occurs in patients with sickle cell disease.)

The spleen, an organ located in the upper left part of the abdomen near the stomach, produces lymphocytes, filters blood, serves as a major reservoir for blood, destroys blood cells that are aged, and has an important function in the filtering, phagocytosis (engulfing) and removal of bacteria from the bloodstream. Asplenic patients run a significantly increased risk of severe sepsis (bloodstream infection), especially from the pneumococcus bacterium.

The prefix "a-" comes from the Greek meaning "not."