The spleen is an important organ in regard to immunological function due to its ability to efficiently destroy encapsulated bacteria.

[1] Common indications for splenectomy include trauma, tumors, splenomegaly or for hematological disease such as sickle cell anemia or thalassemia.

The rest (~25%) of the spleen is known as the white pulp and functions like a large lymph node being the largest secondary lymphoid organ in the body.

[3] Apart from regular lymphatic function the white pulp contains splenic macrophages which are particularly good at destroying (phagocytosis) encapsulated bacteria such as Streptococcus pneumoniae.

It is removed under the following circumstances: The classical cause of traumatic damage to the spleen is a blow to the abdomen during a sporting event.

In cases where the spleen is enlarged due to illness (mononucleosis), trivial activities, such as leaning over a counter or straining while defecating, can cause a rupture.

Vaccination for S. pneumoniae, H. influenza and N. meningitidis should be given pre-operatively if possible to minimize the chance of overwhelming post-splenectomy infection (OPSI), a rapid-developing and highly fatal type of septicaemia.

[9] The post-splenectomy platelet count may rise to abnormally high levels (thrombocytosis), leading to an increased risk of potentially fatal clot formation.

Mild thrombocytosis may be observed after a splenectomy due to the lack of sequestering and destruction of platelets that would normally be carried out by the spleen.