What Causes ITP?

Maybe it started with unexplained bruising, or a nosebleed that lingered longer than it should have. Or maybe nothing seemed wrong at all until a routine blood test turned up a surprisingly low platelet count. Either way, hearing the term immune thrombocytopenia (ITP) for the first time can be overwhelming.

ITP is a rare blood disorder and, more specifically, a platelet disorder. It happens when the immune system mistakenly destroys platelets, the blood cells that help blood clot and stop bleeding. It’s considered a type of autoimmune disease, which is a condition where the immune system turns against the body’s own cells.

So what causes ITP? This article covers the immune mechanisms behind platelet destruction. It also looks at primary versus secondary ITP, common triggers, and who’s more likely to develop this condition.

How Does the Immune System Cause ITP?

ITP develops when the immune system makes antibodies that mistakenly target platelets. These antibodies mark platelets for destruction. Platelets then get cleared out faster than the bone marrow can replace them, leaving fewer of them behind to help blood clot normally.

How Autoantibodies Target Platelets

In most cases, the immune system produces autoantibodies — mainly IgG, a common type of antibody. These autoantibodies attach to proteins on the platelet surface. Once tagged, the platelets get treated like foreign invaders.

The spleen plays a central role here. It’s an organ that filters the blood and is home to immune cells called macrophages. These cells recognize and remove antibody-marked platelets from circulation.

Because so much of this clearing happens there, removing the spleen can sometimes help. This procedure, called a splenectomy, is one option a care team may discuss, usually only after other treatments have been tried.

Why Platelet Production Can’t Keep Up

At the same time, the bone marrow struggles to make enough new platelets to replace the ones being destroyed. The cells responsible for making platelets, called megakaryocytes, can also become targets of the immune attack. This limits how quickly the body can rebuild its platelet supply.

T cells, another part of the immune system, seem to play a role, too. People with ITP often have reduced activity from a type of T cell, called a regulatory T cell, that normally keeps the immune system in check. Without that check in place, the attack on platelets can continue.

A different type of T cell, called a cytotoxic T cell, can add to the problem in its own way. These cells can directly destroy platelets and megakaryocytes, without needing antibodies to mark them first.

Taken together, ITP is increasingly understood as a condition with several distinct mechanisms, not one single cause. Antibody-driven destruction, impaired platelet production, and immune cell involvement can all play a part. The mix varies from person to person.

What Is the Difference Between Primary and Secondary ITP?

ITP is generally grouped into two categories — primary and secondary — based on whether an underlying cause can be identified. Figuring out which type someone has can shape how it’s managed.

ITP is also classified by how long it has been since diagnosis. Newly diagnosed ITP lasts less than three months. Persistent ITP lasts from three to 12 months. Chronic ITP lasts longer than 12 months. Children are more likely than adults to recover during the first several months after diagnosis, while adults are more likely to develop chronic ITP.

What Is Primary ITP?

Primary ITP develops without any identifiable underlying cause. It accounts for about 80 percent of cases.

Because no clear trigger can be found, doctors typically diagnose primary ITP after ruling out other possible causes. This usually involves blood work, physical examination, and a review of medical history and medications

What Is Secondary ITP?

Secondary ITP, on the other hand, develops because of an identifiable underlying condition. This might be an infection, an autoimmune disorder, certain medications, or another illness.

It behaves similarly to primary ITP at the immune level. But treating the underlying cause can sometimes help resolve it.

Who Is at Risk for Developing ITP?

ITP can affect anyone, but certain patterns show up more often in research.

Age and ITP Risk

ITP risk tends to follow two peaks. One is in childhood, when it’s often acute and short-lived. The other is in adults over age 60, when it’s more likely to become chronic.

Sex Differences in ITP Risk

Among younger adults, ITP is diagnosed more often in women than in men. Researchers are still studying why this may be. Hormones such as estrogen may play a role, but the exact reason for this difference is not yet known.

Genetic Susceptibility and the Unknown Trigger for Primary ITP

Genetics may also play a role. Researchers believe some inherited genes may increase a person’s chance of developing ITP. However, most people with ITP do not have a family history of the condition, and inherited cases are uncommon.

Current research suggests this genetic link may matter most for chronic ITP, rather than ITP overall. That could help explain why some cases clear up quickly while others stick around.

Even with all of this research, the exact trigger for primary ITP remains largely unknown. It’s still an active area of study. Understanding these genetic and immune factors may eventually help doctors predict who is more likely to develop the condition.

Your Action Plan

Understanding the causes of ITP can feel like a lot, especially because they vary from person to person. Your best first step is working with your doctors to find out if your ITP is primary or secondary so they can create an appropriate treatment plan.

Be sure to tell your doctor about any recent illnesses, new medications, or vaccinations, as these details may help identify a possible trigger. It’s also important to ask which medications to avoid. For example, nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen can make it harder for your blood to clot when your platelet count is low.

Although living with ITP can be challenging, working closely with your hematologist can help you better understand your condition and develop a treatment plan that’s tailored to your needs.

Join the Conversation

On myITPteam, people share their experiences with immune thrombocytopenia, get advice, and find support from others who understand.

Have you and your care team landed on the cause of your ITP? Let others know in the comments below.