Asplenia is the absence of normal spleen function. It predisposes to some septicemia infections. Therefore, vaccination and antibiotic measures are essential in such cases. There are multiple causes:

- Some people congenitally completely lack a spleen, although this is rare.

- Sickle-cell disease can cause a functional asplenia (or autosplenectomy) by causing infarctions of the spleen during repeated sickle-cell crises.

- It may be removed surgically (known as a splenectomy), but this is rarely performed, as it carries a high risk of infection and other adverse effects. Indications include following abdominal injuries with rupture and hemorrhage of the spleen, or in the treatment of certain blood diseases (Idiopathic thrombocytopenic purpura, hereditary spherocytosis, etc.), certain forms of lymphoma or for the removal of splenic tumors or cysts.

If the splenomegaly underlies hypersplenism, a splenectomy is indicated and will correct the hypersplenism. However, the underlying cause of the hypersplenism will most likely remain; consequently, a thorough diagnostic workup is still indicated, as, leukemia, lymphoma and other serious disorders can cause hypersplenism and splenomegaly. After splenectomy, however, patients have an increased risk for infectious diseases.

Patients undergoing splenectomy should be vaccinated against "Haemophilus influenzae", "Streptococcus pneumoniae", and "Meningococcus". They should also receive annual influenza vaccinations. Long-term prophylactic antibiotics may be given in certain cases.

In cases of infectious mononucleosis splenomegaly is a common symptom and health care providers may consider using abdominal ultrasonography to get insight into a person's condition. However, because spleen size varies greatly, ultrasonography is not a valid technique for assessing spleen enlargement and should not be used in typical circumstances or to make routine decisions about fitness for playing sports.

Splenic diseases include splenomegaly, where the spleen is enlarged for various reasons. On the other hand, a lack of normal spleen function is called asplenia.

Pneumococcal septicemia, or whole-body infection caused by the "Streptococcus pneumoniae" bacteria, has been reported to cause autosplenectomy but is a very rare and poorly understood complication of the infection.

Splenomegaly is an enlargement of the spleen. The spleen usually lies in the left upper quadrant (LUQ) of the human abdomen. Splenomegaly is one of the four cardinal signs of "hypersplenism" which include; some reduction in the number of circulating blood cells affecting granulocytes, erythrocytes or platelets in any combination, a compensatory proliferative response in the bone marrow, and the potential for correction of these abnormalities by splenectomy. Splenomegaly is usually associated with increased workload (such as in hemolytic anemias), which suggests that it is a response to hyperfunction. It is therefore not surprising that splenomegaly is associated with any disease process that involves abnormal red blood cells being destroyed in the spleen. Other common causes include congestion due to portal hypertension and infiltration by leukemias and lymphomas. Thus, the finding of an enlarged spleen, along with caput medusa, is an important sign of portal hypertension.

There is no real treatment for Felty's syndrome, rather the best method in management of the disease is to control the underlying rheumatoid arthritis. Immunosuppressive therapy for RA often improves granulocytopenia and splenomegaly; this finding reflects the fact that Felty's syndrome is an immune-mediated disease. A major challenge in treating FS is recurring infection caused by neutropenia. Therefore, in order to decide upon and begin treatment, the cause and relationship of neutropenia with the overall condition must be well understood. Most of the traditional medications used to treat RA have been used in the treatment of Felty's syndrome. No well-conducted, randomized, controlled trials support the use of any single agent. Most reports on treatment regimens involve small numbers of patients.

Splenectomy may improve neutropenia in severe disease.

Use of rituximab and leflunomide have been proposed.

Use of gold therapy has also been described.

Prognosis is dependent on the severity of symptoms and the patient's overall health.

Absence of effective splenic function or absence of the whole spleen (asplenia) is associated with increased risks of overwhelming post splenectomy infection, especially from polysaccharide encapsulated bacteria and organisms that invade erythrocytes. People without a spleen have a weakened immune system, although other immune organs compensate for the missing spleen. Vaccination against encapsulated bacteria and prophylactic antibiotics can be used to counteract lowered immunity in asplenic patients. Specifically, people without a spleen are recommended to be vaccinated against pneumonia, influenza, Haemophilus influenza type b and meningococci.

Experimental gene therapy exists to treat hereditary spherocytosis in lab mice; however, this treatment has not yet been tried on humans due to all of the risks involved in human gene therapy.

Hepatosplenomegaly (commonly abbreviated HSM) is the simultaneous enlargement of both the liver (hepatomegaly) and the spleen (splenomegaly). Hepatosplenomegaly can occur as the result of acute viral hepatitis, infectious mononucleosis, and histoplasmosis or it can be the sign of a serious and life-threatening lysosomal storage disease. Systemic venous hypertension can also increase the risk for developing hepatosplenomegaly, which may be seen in those patients with right-sided heart failure.

Banti's syndrome (also known as Banti's disease), named for is Guido Banti., is a chronic congestive enlargement of the spleen resulting in premature destruction of the red blood cells by the spleen.

Enlargement of spleen, ascites, jaundice, and the result of destruction of various blood cells by spleen – anemia, leukopenia, thrombocytopenia, gastrointestinal bleeding – may constitute the presenting symptoms.

Hereditary spherocytosis is the most common disorder of the red cell membrane and affects 1 in 2,000 people of Northern European ancestry. According to Harrison's Principles of Internal Medicine, the frequency is at least 1 in 5,000.

The protective effect of sickle-cell trait does not apply to people with sickle cell disease; in fact, they are more vulnerable to malaria, since the most common cause of painful crises in malarial countries is infection with malaria. It has therefore been recommended that people with sickle-cell disease living in malarial countries should receive anti-malarial chemoprophylaxis for life.

From birth to five years of age, penicillin daily, due to the immature immune system that makes them more prone to early childhood illnesses is recommended. Dietary supplementation of folic acid had been previously recommended by the WHO. A 2016 Cochrane review of its use found "the effect of supplementation on anaemia and any symptoms of anaemia remains unclear" due to a lack of medical evidence.

Often, no treatment is required or necessary for reactive thrombocytosis. In cases of reactive thrombocytosis of more than 1,000x10/L, it may be considered to administer daily low dose aspirin (such as 65 mg) to minimize the risk of stroke or thrombosis.

However, in primary thrombocytosis, if platelet counts are over 750,000 or 1,000,000, and especially if there are other risk factors for thrombosis, treatment may be needed. Selective use of aspirin at low doses is thought to be protective. Extremely high platelet counts in primary thrombocytosis can be treated with hydroxyurea (a cytoreducing agent) or anagrelide (Agrylin).

In Jak-2 positive disorders, ruxolitinib (Jakafi) can be effective.

Corticosteroids and immunoglobulins are two commonly used treatments for warm antibody AIHA. Initial medical treatment consists of prednisone. If ineffective, splenectomy should be considered.

If refractory to both these therapies, other options include rituximab, danazol, cyclosphosphamide, azathioprine, or ciclosporin.

High-dose intravenous immune globulin may be effective in controlling hemolysis, but the benefit is short lived (1–4 weeks), and the therapy is very expensive.

Treatment consists of frequent blood transfusions and chelation therapy. Potential cures include bone marrow transplantation and gene therapy.

Overall, hemoglobin C disease is one of the more benign hemoglobinopathies. Mild-to-moderate reduction in RBC lifespan may accompany from mild hemolytic anemia. Individuals with hemoglobin C disease have sporadic episodes of musculoskeletal (joint) pain. People with hemoglobin C disease can expect to lead a normal life.

Felty's syndrome, also called Felty syndrome, (FS) is rare autoimmune disease characterized by the triad of rheumatoid arthritis, splenomegaly and neutropenia. The condition is more common in those aged 50–70 years, specifically more prevalent in females than males, and more so in Caucasians than those of African descent. It is a deforming disease that causes many complications for the individual.

Treatment primarily consists of reducing eosinophil levels and preventing further damage to organs. Corticosteroids, such as Prednisone, are good for reducing eosinophil levels and antineoplastics are useful for slowing eosinophil production. Surgical therapy is rarely utilised, however splenectomy can reduce the pain due to spleen enlargement. If damage to the heart (in particular the valves), then prosthetic valves can replace the current organic ones. Follow-up care is vital for the survival of the patient, as such the patient should be checked for any signs of deterioration regularly. After promising results in drug trials (95% efficiency in reducing blood eosinophil count to acceptable levels) it is hoped that in the future hypereosinophilic syndrome, and diseases related to eosinophils such as asthma and eosinophilic granulomatosis with polyangiitis, may be treated with the monoclonal antibody Mepolizumab currently being developed to treat the disease. If this becomes successful, it may be possible for corticosteroids to be eradicated and thus reduce the amount of side effects encountered.

Beta thalassemia is a hereditary disease allowing for a preventative treatment by carrier screening and prenatal diagnosis. It can be prevented if one parent has normal genes, giving rise to screenings that empower carriers to select partners with normal hemoglobin. A study aimed at detecting the genes that could give rise to offspring with sickle cell disease. Patients diagnosed with beta thalassemia have MCH ≤ 26 pg and an RDW < 19. Of 10,148 patients, 1,739 patients had a hemoglobin phenotype and RDW consistent with beta thalassemia. After the narrowing of patients, the HbA2 levels were tested presenting 77 patients with beta thalassemia. This screening procedure proved insensitive in populations of West African ancestry because of the indicators has high prevalence of alpha thalassemia. Countries have programs distributing information about the reproductive risks associated with carriers of haemoglobinopathies. Thalassemia carrier screening programs have educational programs in schools, armed forces, and through mass media as well as providing counseling to carriers and carrier couples. Screening has showed reduced incidence; by 1995 the prevalence in Italy reduced from 1:250 to 1:4000, and a 95% decrease in that region. The decrease in incidence has benefitted those affected with thalassemia, as the demand for blood has decreased, therefore improving the supply of treatment.

Excellent for single-focus disease. With multi-focal disease 60% have a chronic course, 30% achieve remission and mortality is up to 10%.

The European Medicines Agency (EMA) estimated the prevalence of HES at the time of granting orphan drug designation for HES in 2004 at 1.5 in 100,000 people, corresponding to a current prevalence of about 8,000 in the EU, 5,000 in the U.S., and 2,000 in Japan.

Patients who lack chronic heart failure and those who respond well to Prednisone or a similar drug have a good prognosis. However, the mortality rate rises in patients with anaemia, chromosomal abnormalities or a very high white blood cell count.

For those with type-I and most type-III, enzyme replacement treatment with intravenous recombinant glucocerebrosidase can decrease liver and spleen size, reduce skeletal abnormalities, and reverse other manifestations. This treatment costs about US$200,000 annually for a single person and should be continued for life. The rarity of the disease means dose-finding studies have been difficult to conduct, so controversy remains over the optimal dose and dosing frequency. Due to the low incidence, this has become an orphan drug in many countries, meaning a government recognizes and accommodates the financial constraints that limit research into drugs that address a small population.

The first drug for Gaucher's was alglucerase (Ceredase), which was a version of glucocerebrosidase that was harvested from human placental tissue and then modified with enzymes. It was approved by the FDA in 1991 and has been withdrawn from the market due to the approval of similar drugs made with recombinant DNA technology instead of being harvested from tissue; drugs made recombinantly are preferable, since there is no concern about diseases being transmitted from the tissue used in harvesting, there are fewer risks of variations in enzyme structure from batch to batch, and they are less expensive to manufacture.

Available recombinant glucocerebrosidases are:

- Imiglucerase (approved in 1995)

- Velaglucerase (approved in 2010)

- Taliglucerase alfa (Elelyso) (approved in 2012)

- Eliglustat (Cerdelga) (approved in 2014)

Miglustat is a small molecule, orally available drug that was first approved for Gaucher's Disease in Europe in 2002. It works by preventing the formation of glucocerebroside, the substance that builds up and causes harm in Gaucher's. This approach is called substrate reduction therapy.

Usually no treatment is needed. Folic acid supplementation may help produce normal red blood cells and improve the symptoms of anemia