Immune thrombocytopenia causes

Last updated June 23, 2025, by Lindsey Shapiro, PhD
Fact-checked by Joana Carvalho, PhD

The rare bleeding disorder immune thrombocytopenia (ITP) arises when the immune system mistakenly attacks healthy platelets — the cell fragments needed to facilitate blood clotting — but exactly why this happens is not known in most cases.

People with ITP have low platelet counts, known as thrombocytopenia, which leaves them susceptible to symptoms of excessive internal or external bleeding.

Most of the time, there’s no established cause for this autoimmune thrombocytopenia. But in some cases, things like infections, medications, or other diseases can affect the immune system in ways that are believed to trigger ITP. Various other risk factors such as age, sex, or genetics may also influence a person’s susceptibility to develop ITP.

Primary causes of immune thrombocytopenia

ITP is an autoimmune disease, in which the immune system that’s normally designed to attack harmful invaders like viruses and bacteria inappropriately attacks healthy parts of the body.

In the case of ITP, platelets, or the circulating cell fragments that help blood clot after an injury, are the targets of these autoimmune attacks. Immune B-cells and plasma cells generate self-reactive antibodies that bind to proteins on the surface of platelets, marking them for destruction by immune macrophages in the spleen. These self-reactive antibodies can also target platelet precursors, called megakaryocytes, in the bone marrow to inhibit further platelet production.

More recent studies have also shown the involvement of several subtypes of immune T-cells in this process — including in the promotion of autoantibody production and in the destruction of platelets and megakaryocytes.

As with many autoimmune diseases, doctors usually don’t know what causes ITP, and there’s no definitive reason why the immune system launches these mistaken attacks against platelets.

The majority of ITP cases — about 80% — are considered primary, or idiopathic, meaning platelets are the only target of the autoimmune attacks and there are no clear causes of ITP.

Secondary causes and triggers

While immune problems are the primary causes of ITP, there are other factors that can trigger the disease. In about 20% of cases, ITP is considered secondary, where it is associated with another underlying condition that predisposes the immune system to launch its attacks against platelets.

Possible secondary ITP triggers include:

• viral infections, including those driven by viruses that cause chickenpox, hepatitis C, and HIV
• bacterial infections, such as those caused by Helicobacter pylori
• certain medications, among them some antibiotics, antivirals, anti-inflammatory drugs, and other drugs
• vaccinations
• other autoimmune diseases, like lupus, antiphospholipid syndrome, or Evans syndrome
• cancer, especially blood cancers like leukemia or lymphoma that cause abnormal immune cell growth
• pregnancy.

These secondary causes of ITP are believed to prime the immune system in various ways to be overly reactive or to lose immune tolerance, the process by which it is usually able to recognize the body’s own healthy tissues and leave them unharmed. Medications can trigger ITP when they bind to platelets, creating a foreign target that the immune system wants to mark for destruction.

Some infections could trigger ITP through a process known as molecular mimicry, in which the immune system generates antibodies to fight off a harmful invader that then cross-reacts with platelets and causes their destruction. ITP in children commonly appears shortly after a viral infection and gets better on its own, without specific ITP treatment, within a few months.

Important to note is that while certain vaccines, including the one for measles-mumps-rubella, are possible secondary ITP causes, this is very rare. It is more likely that ITP would occur after a natural infection with one of these disease-causing agents.

Immune thrombocytopenia risk factors

Certain factors may influence a person’s likelihood of developing ITP, but these can depend on whether the disease is acute — resolving within a few weeks or months — or chronic, where the condition persists longer-term.

These ITP risk factors may include age and sex, as well as co-occurring conditions or exposure to them:

• Age can be a potential risk factor, as ITP generally is more common in children than in adults. Acute ITP primarily affects children, but chronic ITP is more prevalent in adults.
• Sex also may play a role in risk, with ITP being 2-3 times more likely to occur in females than males, starting during adolescence and adulthood. The disease occurs equally in boys and girls during childhood.
• Having another autoimmune disease may be a risk factor.
• Another possible risk factor is exposure to infectious agents or medications that can cause ITP. Acute ITP in particular is commonly associated with a recent viral infection.

ITP is not considered to be an inherited disorder and it does not usually run in families. Some studies have identified genetic factors that may influence a person’s risk of developing ITP, particularly in immune-related genes; their exact role in the disease has not been established, however.

While lifestyle factors are not thought to directly cause ITP, certain habits, including excessive alcohol consumption and smoking, can affect platelet levels and worsen the disease or make it more likely for a person to have ITP symptoms.

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