Heparin-Induced Thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is a rare, potentially life-threatening issue that happens when your immune system reacts to the blood thinner heparin. The reaction causes platelets in your blood to make more blood clots than your body needs.

Platelets are tiny cell fragments in your blood vessels. They form blood clots to control bleeding. In HIT, your body makes more blood clots than it needs to control bleeding. That can lead to thrombosis.

In thrombosis, blood clots reduce or block your blood flow. They can also break free and travel to other parts of your body:

• Clots in a vein deep in your body, often a leg vein, can reduce or block blood flow. This is deep vein thrombosis, or DVT.
• A clot that’s lodged in a vein can break loose and travel to your lungs, leading to a pulmonary embolism (PE).
• Clots that form in an artery can block blood flow to vital organs, like your brain or heart, leading to a stroke or heart attack.

HIT may also lead to thrombocytopenia. This is when you don’t have enough platelets to stop bleeding. In HIT, the process involved in making blood clots reduces the number of platelets in your blood. Fewer platelets mean fewer blood clots. Fewer blood clots increases the chance you’ll bleed more than usual or have bleeding that’s hard to stop.

If you take heparin, your healthcare provider will check platelet levels. Low levels of platelets after taking heparin may be a sign of HIT. This condition is also known as heparin-induced thrombocytopenia thrombosis (HITT).

Types of this condition

The two types of heparin-induced thrombocytopenia are HIT I and HIT II:

• HIT I: In this type, your platelet levels drop after you take heparin and then return to normal. HIT I doesn’t increase your risk of blood clots.
• HIT II: This type does increase your risk of blood clots that may lead to thrombocytopenia and thrombosis.

Heparin-induced thrombocytopenia symptoms

About half of the people with HIT develop a new blood clot. They may develop deep vein thrombosis or a pulmonary embolism. These forms of thrombosis are life-threatening issues. You should get emergency medical attention immediately if you take heparin and experience any of these symptoms:

• Pain, swelling, redness or tenderness in your arm or leg
• Sudden sharp pain in your chest
• Feeling faint, dizzy or light-headed
• Rapid heartbeat
• Coughing and wheezing
• Feeling out of breath
• Excessive sweating
• Fever and chills

HIT may also lead to excessive bleeding. One of the first symptoms is a cut or nosebleed that won’t stop bleeding. Other symptoms include:

• Bleeding gums
• Blood in pee or poop
• Bruises

Excessive bleeding can also be a medical emergency.

HIT symptoms may appear at different times:

• Early-onset HIT: You may have symptoms if you’ve taken heparin within the past three months. Your symptoms may start one to three days after your treatment.
• Refractory HIT: In this case, you have HIT symptoms that continue after you stop taking heparin.
• Delayed onset HIT: You only have symptoms after you stop taking heparin. Your symptoms may start five or more days after you finish taking the medication.

What causes heparin-induced thrombocytopenia?

HIT occurs when heparin combines with PF4, a protein in your platelets. The combination, known as heparin-PF4, sets off a series of events that lead to thrombosis or thrombocytopenia.

First, your immune system makes antibodies that bind to heparin-PF4. Next, the bundle of heparin-PF4 and antibodies binds to your platelets. This causes your platelets to stick together and form clumps that become blood clots.

At the same time, your platelets release more PF4, the protein that triggers your immune system to make more antibodies. This causes heparin-PF4 to bind to more platelets, which react by forming more blood clots.

What are the risk factors for heparin-induced thrombocytopenia?

Risk factors for HIT include:

• Your sex: HIT is more common in women.
• Your medication: Some studies suggest that the form of heparin you take may reduce your risk of HIT. More research is needed to know for sure.
• Your medical treatment: Orthopedic surgery, heart surgery and cardiopulmonary bypass are all associated with an increased risk of developing heparin-induced thrombocytopenia.

Complications

HIT may lead to serious complications like:

• Heart attack: This is when a blood clot blocks your coronary artery. It may also happen if you develop thrombocytopenia, which may decrease blood flow to your heart.
• Pulmonary embolism: This is a blood clot in your lungs.
• Severe internal bleeding: Thrombocytopenia may cause gastrointestinal bleeding or bleeding in your brain. Bleeding into your brain is a life-threatening issue.
• Skin necrosis: Blood clots that affect blood flow to your skin may affect skin near the heparin injection site.
• Transient ischemic attack or stroke: This can happen if a clot forms in your brain or in the carotid artery that supplies blood to your brain.

Very rarely, a blood clot in your adrenal glands may cause an adrenal crisis.

How do doctors diagnose HIT?

Your healthcare provider will do blood tests to confirm you have HIT. Specific tests are:

• Platelet levels: Your platelet levels reveal whether you have thrombocytopenia.
• Clot formation: A D-dimer test can show if your blood is forming clots.
• PF4 antibody levels: The amount of PF4 antibody levels in your blood can confirm your immune system’s reaction. Providers use this test to confirm that you have HIT.

What is the 4Ts test in heparin-induced thrombocytopenia?

The 4Ts test is a scoring system that helps healthcare providers estimate the chance you have HIT. The scoring system gives providers enough information about your condition to start treatment before they make a final diagnosis.

In the 4Ts test, providers assign a score (from 0 to 2 points) for the following criteria:

• Thrombocytopenia: This is low levels of platelets.
• Timing: Your provider checks when your platelet levels drop. This shows how quickly your immune system reacts to heparin.
• Thrombosis: They’ll look for blood clot symptoms and signs.
• Thrombocytopenia cause: Other conditions cause thrombocytopenia. Your provider may do tests to rule out other causes.

The higher the score, the greater the likelihood that you have HIT.

How doctors treat heparin-induced thrombocytopenia

Your healthcare provider will switch to a different blood thinner that won’t cause an immune system reaction. You may receive heparin alternatives like:

• Direct thrombin inhibitors
• Fondaparinux
• Direct oral anticoagulants, like factor Xa inhibitors

They may change to warfarin, another blood-thinning medication, once tests show you have normal platelet levels.

You may have additional treatment for thrombocytopenia. This is when HIT causes excessive bleeding. Treatment to manage bleeding may include:

• Steroids: This medication boosts platelet production.
• Blood transfusion: This treatment temporarily increases your platelet levels.

When should I seek care?

Contact your provider or go to the emergency room if you have symptoms like sharp chest pain, sudden pain or swelling in your arm or leg, or if you feel dizzy. These symptoms may mean a blood clot is blocking an artery. You should also seek medical attention if you have bleeding that you can’t control.

What can I expect if I have heparin-induced thrombocytopenia?

You may need to take non-heparin blood thinners for a month or more, depending on your situation. Your provider will schedule regular follow-ups to check for blood clots. They’ll also check for side effects that can happen when you switch from heparin to another medication.

Having HIT means you shouldn’t take heparin. Make sure all of your providers know your medical history. Ask your healthcare provider if you should carry a medical alert card.