Primary thrombocytopenia is an autoimmune disorder that causes a low number of platelets in the blood. Other names for it are immune thrombocytopenia and ITP.

Platelets are specialized blood cells that help stop bleeding by accelerating clotting. When a person has a low number of platelets, they may have extensive bleeding, including internal bleeding, after an injury.

Primary thrombocytopenia varies in severity, and in many cases, doctors can treat it.

In this article, we compare primary and secondary thrombocytopenia and describe the symptoms, causes, treatments, and outlook for people with this disorder.

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Primary thrombocytopenia is an autoimmune disorder that causes low levels of platelets in the blood. Platelets support blood vessel walls and help with clotting.

A healthy number of platelets is 150,000–400,000 per microliter of blood. If a person has fewer than 100,000 platelets per microliter of blood, with no other known cause, they may have primary thrombocytopenia.

People with thrombocytopenia may have purple or red spots or patches of skin due to bleeding just below the skin’s surface. Smaller spots from this type of bleeding are called purpura, and larger patches are bruises, also called ecchymoses.

People with thrombocytopenia may also experience extreme bleeding, such as a heavy nose bleed. And menstrual bleeding may be unusually heavy. In severe cases, gastrointestinal bleeding may lead to blood in stool and urine.

“Primary” thrombocytopenia refers to the body’s immune cells destroying platelets for no clear reason. Experts do not understand why this occurs.

Lymphocytes are a type of white blood cell in the bone marrow, spleen, and other areas of the body. They become stimulated to produce antibodies, which attach to platelets.

The immune system then attacks the platelets because it mistakenly recognizes them as foreign. This leaves fewer platelets, making it more difficult for blood to clot, which can lead to excessive bleeding.

If a person has thrombocytopenia as a result of another disorder, it is “secondary“.

This means that the immune system is attacking platelets because it is trying to fight off another condition. This may be an autoimmune disorder such as systemic lupus erythematosus or a blood disorder such as chronic lymphocytic leukemia.

The symptoms of thrombocytopenia vary from person to person.

Some people have a higher tolerance for low platelet levels, and they may not bruise or bleed as extensively. A person may have no symptoms or only have symptoms when their platelet count is very low.

The symptoms may include:

  • bleeding from the gums
  • frequent nose bleeds that last and are hard to stop
  • spontaneous or easy bruising
  • a rash of small red dots, which indicate bleeding caused by broken or leaking blood vessels
  • prolonged, heavy menstrual bleeding
  • blood blisters on the insides of the cheeks
  • extreme fatigue, low mental and physical energy, and depression
  • signs of internal bleeding, such as blood in the urine, stool, or vomit, although this is less common
  • rarely, bleeding in the brain, which is called intracranial hemorrhage

Thrombocytopenia occurs when the immune system attacks healthy platelets because it has incorrectly identified them as harmful foreign substances called antigens.

In a healthy body, the immune system produces antibodies in response to antigens, which may be bacterial or viral.

If a person has thrombocytopenia, blood cells called lymphocytes produce antibodies that attach to the surfaces of platelets. The immune system recognizes these platelets as a threat, and cells called tissue macrophages ingest and destroy the antibody-coated platelets.

The antibodies may also bond to large bone marrow cells called megakaryocytes. This can result in the bone marrow producing fewer platelets.

Experts are still unsure why the immune system responds as it does in a person with thrombocytopenia.

In children, thrombocytopenia sometimes follows an acute viral infection, such as chickenpox. In these cases, antibodies created to fight the infection may mistakenly lead to the attack on platelets.

The disorder does not appear to be hereditary, as it is quite rare for more than one family member in more than one generation to have thrombocytopenia.

For thrombocytopenia, a doctor may recommend:

  • Corticosteroids: These are the most effective, first-line treatment. Options such as methylprednisolone, prednisone, or dexamethasone work by suppressing the clearance of antibody-covered platelets and may increase the production of platelets.
  • Platelet transfusion: If treatment with corticosteroids is not successful, a doctor may recommend immunoglobulin infusion therapy, based on the person’s platelet count and bleeding. This is generally reserved for emergency situations, as the body is likely to destroy the transfused platelets quickly.
  • Thrombopoietin receptor agonists: These drugs work by stimulating the production of platelets to overcome the rate at which the immune system is destroying them. Examples include avatrombopag (Doptelet), eltrombopag (Promacta), and romiplostim (Nplate).
  • Surgery: A doctor may recommend the removal of the spleen if drug-based approaches do not work.

People with thrombocytopenia have an increased risk of severe internal or external bleeding, which can be life threatening. However, most people with the disorder have mild to moderate symptoms.

The outlook for children with thrombocytopenia is especially good, with 80% experiencing spontaneous remission.

The rate of mortality is higher in older adults for whom treatment has been ineffective.

Primary thrombocytopenia is an autoimmune disorder, that causes the immune system to attack platelets in blood. This leads to low numbers of platelets and a decreased capacity to produce new ones.

This can lead to excessive bleeding, including menstrual bleeding, and bruising.

Experts do not know what causes the immune system to attack healthy platelets in a person with primary thrombocytopenia.

The treatment usually involves corticosteroids, but there are also other drug-based and surgical options. In emergency situations, a transfusion may be necessary.

The outlook for someone with this disorder depends on its severity.