Antithrombin Deficiency

Antithrombin (antithrombin III) deficiency is a blood clotting problem that can put you at risk for a dangerous blood clot. When you have this deficiency, clotting can continue without enough antithrombin to stop it. This is why you can get a deep vein thrombosis (DVT) in your leg or a pulmonary embolism in your lung.


What is antithrombin deficiency?

Antithrombin deficiency (or antithrombin III deficiency) is a blood clotting disorder that makes you more likely to get abnormal blood clots. People with this problem are at a high risk for deep vein thrombosis (a blood clot in any deep vein of the body) and pulmonary embolism (a clot that ends up in your lungs).

Antithrombin helps keep your blood from clotting excessively. When your antithrombin isn’t working right, clotting can keep going without antithrombin stopping it. When you don’t have enough antithrombin, it’s like starting to fill a bathtub with water and then walking away. Someone needs to be there to turn the water off to keep the bathtub from overflowing, just like the antithrombin needs to stop the clotting before it goes on too long.


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How common is antithrombin deficiency?

Antithrombin deficiency is rare. One person in every 2,000 to 3,000 people has antithrombin deficiency.

Symptoms and Causes

What are the symptoms?

Different people with antithrombin deficiency may have different symptoms, but your first blood clot usually happens before age 40. The most common symptoms include:

Although it’s not as common, clots can also happen in veins in your brain and abdomen.


What causes antithrombin deficiency?

People who have a mutation on their SERPINC1 gene have antithrombin deficiency. You can inherit this mutation from one of your parents, but those who are born with this mutation won’t necessarily get a blood clot. There is a 50% chance of passing the mutation on to each child you have, regardless of their gender. Unfortunately, babies who inherit antithrombin deficiency from both parents usually don’t survive.

Diagnosis and Tests

How is antithrombin deficiency diagnosed?

To make a diagnosis, your provider will want:

  • Physical exam.
  • Medical history.
  • A blood test that specifically measures antithrombin levels.

Management and Treatment

How is antithrombin deficiency treated?

After you’ve had a clot, your provider may want you to take warfarin (Coumadin®), a blood thinner, for a few months or possibly long-term. People who have antithrombin deficiency but haven’t had a blood clot don’t need to take blood thinners.

Because 3% to 50% of pregnant people with an antithrombin deficiency get blood clots, your provider may decide to give you heparin injections during pregnancy to prevent blood clots during that special time.

How do I take care of myself?

Be sure to keep all of your appointments with your provider. Because taking warfarin or heparin can cause bleeding, your provider will want to make sure you’re getting the right amount of medicine. A prothrombin time or PT test can tell your provider if your warfarin dose is correct. Your provider can adjust your warfarin dose so you don’t get a bad clot, but you don’t bleed too much either.


How can I reduce my risk?

If you have antithrombin deficiency, you can reduce your risk of blood clots in a few ways:

Other things that put you at risk for blood clots include trauma, surgery, pregnancy, childbirth and aging. If you need surgery or are giving birth, your provider can give you a special antithrombin concentrate through an IV in your arm.

How can I prevent antithrombin deficiency?

You can’t change the genes you got from your parents, so you can’t prevent inherited antithrombin deficiency.

Outlook / Prognosis

What can I expect if I have antithrombin deficiency?

One of every two to three people with this problem may develop blood clots in adulthood. Your risk of clots is higher if you have surgery or don’t move your body enough. As you get older, that increases your risk, too. If you have antithrombin deficiency, unusual blood clots can develop during pregnancy or after your baby is born.

How long does antithrombin deficiency last?

Since hereditary antithrombin deficiency is something you’re born with, it’s part of your genetic makeup for life.

Outlook for antithrombin deficiency

Your prognosis will depend on whether you’ve had blood clots or not. Taking blood thinners long-term may prevent recurrent blood clots.

Living With

How do I take care of myself?

You should know the warning signs of deep vein thrombosis and a pulmonary embolism so you can get help quickly. If you’re on warfarin or other blood thinners, which can carry a risk of bleeding, be careful when using sharp objects. You may also want to avoid sports that can put you at risk for injury.

When should I see my healthcare provider?

Contact your provider if you have a diagnosis of deep vein thrombosis. It’s important to treat deep vein thrombosis because the blood clot in your leg can travel to your lungs (pulmonary embolism). When you’re taking warfarin, tell your provider if you’ve fallen or are having unusual bleeding.

When should I go to the ER?

If you have a pulmonary embolism, or if you think you have deep vein thrombosis but cannot contact your healthcare provider, you should go to the ER to get treatment right away. You should also get help if you have a head injury, are throwing up blood or can’t stop bleeding while you’re on warfarin.

What questions should I ask my doctor?

  • Do I need to take warfarin or another blood thinner?
  • Should my family find out if they have antithrombin deficiency?

A note from Cleveland Clinic

When you have antithrombin deficiency, it’s a good idea for you and your loved ones to know the signs of deep vein thrombosis and a pulmonary embolism. If you know what to look for, you can quickly identify what’s happening and get help faster. Watching your weight and staying active can help keep your body from making problematic blood clots. This gives you some control over what antithrombin deficiency can do.

Medically Reviewed

Last reviewed by a Cleveland Clinic medical professional on 11/23/2021.

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