Asplenia refers to the absence of normal spleen function and is associated with some serious infection risks. Hyposplenism is used to describe reduced (hypo-) splenic functioning, but not as severely affected as with asplenism. Functional asplenia occurs when splenic tissue is present but does not work well (e.g. sickle-cell disease, polysplenia) -such patients are managed as if asplenic-, while in anatomic asplenia, the spleen itself is absent. Causes
Congenital
Congenital asplenia is rare. There are two distinct types of genetic disorders: heterotaxy syndrome and isolated congenital asplenia. polysplenia

Acquired
Acquired asplenia occurs for several reasons:

Following splenectomy due to splenic rupture from trauma or because of tumor
After splenectomy with the goal of interfering with splenic function, as a treatment for diseases (e.g. idiopathic thrombocytopenic purpura, thalassemia, spherocytosis), in which the spleens usual activity exacerbates the disease
After splenectomy with the goal of arresting the progression of cancers (Chronic lymphocytic leukemia, Hodgkins disease (starting in the 1970s), non-Hodgkin lymphoma)
Due to underlying diseases that destroy the spleen (autosplenectomy), e.g. sickle-cell disease. Celiac disease: unknown physiopathology. In a 1970 study, it was the second most common cause of abnormalities of red blood cells linked to hyposplenism, after surgical splenectomy. Functional asplenia
Functional asplenia can occur when patients with metabolic or haematological disorders have their splenic tissue organisation altered. This can lead to results similar to those seen in patients who have undergone a splenectomy e.g. becoming infected with encapsulated bacteria such as Haemophilus influenzae, Streptococcus pneumoniae and Neisseria meningitidis.
Patients who have some form of asplenia have an increased susceptibility to these encapsulated bacterial infections mainly because they lack IgM memory B cells and their non-adherence to polysaccharide vaccines. Furthermore, there is a deficiency of other splenic cells e.g. splenic macrophages. This combined with the lack of B cells can provide an environment favourable for the development of bacterial infections. Partial splenectomy and preservation of splenic function
In an effort to preserve some of the spleens protective roles, attempts are now often made to preserve a small part of the spleen when performing either surgical subtotal (partial) splenectomy, or partial splenic embolization. This may be particularly important in poorer countries where protective measures for patients with asplenia are not available. However, it has been advised that preoperative vaccination is advisable until the remnant splenic tissue can reestablish its function. Risks
Asplenia is a form of immunodeficiency, increasing the risk of sepsis from polysaccharide encapsulated bacteria, and can result in overwhelming post splenectomy infection (OPSI), often fatal within a few hours. In particular, patients are at risk from Streptococcus pneumoniae, Haemophilus influenzae, and meningococcus. The risk is elevated as much as 350–fold.The increased risk of infection is due to inability to clear opsonised bacteria from circulating blood.