Antithrombin Deficiency: The Genetic Blood Clotting Disorder Explained
Updated: 2 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: September 2026
TL;DR
Antithrombin deficiency (also called antithrombin III deficiency) is a rare inherited blood clotting disorder that makes abnormal blood clots more likely. It affects about 1 in every 2,000 to 3,000 people and is caused by a mutation on the SERPINC1 gene inherited from one parent. The two most common complications are deep vein thrombosis (DVT) and pulmonary embolism, with the first blood clot usually appearing before age 40. Blood thinners like warfarin treat clots after they occur, and pregnancy-related clot risk (3%–50%) can be managed with heparin injections.
Quick Answer
What it is: Antithrombin deficiency is a blood clotting disorder caused by a SERPINC1 gene mutation that is inherited from one parent, with a 50% chance of passing it to each child.
How common: It is rare, affecting about 1 in every 2,000 to 3,000 people, and puts you at high risk for deep vein thrombosis (DVT) and pulmonary embolism.
Onset: Your first blood clot usually happens before age 40, and one of every two to three people with the deficiency may develop blood clots in adulthood.
Treatment: Treatment after a clot is a blood thinner such as warfarin; pregnant women with the deficiency may receive heparin injections because 3% to 50% of them develop clots.
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. Think of it 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 antithrombin needs to stop the clotting before it goes on too long.
How Common Is Antithrombin Deficiency?
Antithrombin deficiency is rare. One person in every 2,000 to 3,000 people has antithrombin deficiency.
Prevalence statistic | Figure |
People affected | 1 in 2,000 to 3,000 |
Chance of passing the mutation to each child | 50% |
First blood clot typically occurs | Before age 40 |
People who may develop blood clots in adulthood | 1 in 2 to 3 |
Pregnant women with the deficiency who get clots | 3% to 50% |
What Are the Symptoms of Antithrombin Deficiency?
Different people with antithrombin deficiency may have different symptoms, but your first blood clot usually happens before age 40.
Symptom | Description |
Deep vein thrombosis (DVT) | The most common presentation — a blood clot in any deep vein of the body, most often the leg |
Pulmonary embolism | A clot that ends up in your lungs |
Brain vein clots | Less common — clots can happen in veins in the brain |
Abdominal vein clots | Less common — clots can happen in veins in the 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.
Is Antithrombin Deficiency Genetic?
Yes. You can inherit the SERPINC1 mutation from one of your parents, and there is a 50% chance of passing the mutation on to each child you have, regardless of their sex.
Being born with the mutation doesn't guarantee a blood clot — carriers won't necessarily get one. Unfortunately, babies who inherit antithrombin deficiency from both parents usually don't survive.
Inheritance scenario | Outcome |
Mutation from one parent | You have the deficiency, but won't necessarily get a blood clot |
Passed to each child | 50% chance, regardless of sex |
Mutation from both parents | Usually fatal in newborns |
How Is Antithrombin Deficiency Diagnosed?
To make a diagnosis, your provider will want a physical exam, a review of your medical history, and a blood test that specifically measures antithrombin levels.
Diagnostic step | Purpose |
Physical exam | Identifies signs of abnormal clotting |
Medical history | Reveals prior clots and family history |
Antithrombin blood test | Specifically measures antithrombin levels |
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 women 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.
Treatment situation | Approach |
After a blood clot | Warfarin (Coumadin) for a few months or possibly long-term |
Never had a blood clot | No blood thinners needed |
During pregnancy | Heparin injections may prevent clots (3%–50% clot risk) |
Before surgery or childbirth | Special antithrombin concentrate through an IV |
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 (PT test) can tell your provider if your warfarin dose is correct — they can adjust your dose so you don't get a bad clot but don't bleed too much either.
You should know the warning signs of deep vein thrombosis and 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.
What Is the Outlook for 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.
Your prognosis will depend on whether you've had blood clots or not. Taking blood thinners long-term may prevent recurrent blood clots.
Outlook factor | Detail |
Lifelong | Part of your genetic makeup since birth |
Adult clot risk | 1 in 2 to 3 people develop clots in adulthood |
Risk increases with | Surgery, inactivity, and aging |
Pregnancy/postpartum | Unusual clots can develop |
Prevention of recurrence | Long-term blood thinners |
How Can I Reduce My Risk of Blood Clots?
If you have antithrombin deficiency, you can reduce your risk of blood clots in a few ways:
Risk-reduction step | Reason |
Avoid birth control pills | Estrogen increases clot risk |
Avoid hormone therapy | Increases clot risk |
Don't be inactive for long periods | Movement helps prevent clotting |
Don't smoke or use tobacco | Smoking increases clot risk |
Stay at a healthy weight | Weight management reduces risk |
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.
Can Antithrombin Deficiency Be Prevented?
You can't change the genes you got from your parents, so you can't prevent inherited antithrombin deficiency. What you can prevent are the conditions that trigger dangerous clots by managing the risk factors above.
When Should I See My Healthcare Provider?
Contact your provider if you have a diagnosis of deep vein thrombosis. It's important to treat DVT 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?
Go to the ER right away if you have a pulmonary embolism, or if you think you have DVT but cannot contact your healthcare provider. 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.
Situation | Action |
Pulmonary embolism | ER immediately |
Suspected DVT with no provider contact | ER immediately |
Head injury while on warfarin | ER immediately |
Vomiting blood while on warfarin | ER immediately |
Can't stop bleeding while on warfarin | ER immediately |
Fall while on warfarin | Tell your provider |
Unusual bleeding while on warfarin | Tell your provider |
Conclusion
Antithrombin deficiency is a rare but serious inherited blood clotting disorder — about 1 in 2,000 to 3,000 people carry the SERPINC1 mutation that makes their blood more prone to forming dangerous clots. The condition is a genetic lottery drawn at conception, but it is not a guarantee of illness: many carriers never develop a clot, while one in two to three people experience clots in adulthood, usually for the first time before age 40.
The real danger lies in what the clots do — deep vein thrombosis in the leg can travel to the lungs and become a life-threatening pulmonary embolism. The encouraging news is that treatment is straightforward and effective: blood thinners like warfarin after a clot, PT-test-monitored dosing to balance clotting and bleeding, heparin protection during pregnancy, and even antithrombin concentrate by IV before surgery or childbirth. Everyday choices — staying active, avoiding tobacco and hormonal medications, and maintaining a healthy weight — put meaningful control back in your hands.
If you or a family member has had an unusual blood clot before age 40, ask your provider about antithrombin testing and whether relatives should be screened — the mutation carries a 50% chance of passing to each child. Knowing your status, and knowing the emergency signs of DVT and pulmonary embolism, could save a life.
FAQ
What is antithrombin deficiency?
Antithrombin deficiency (antithrombin III deficiency) is a blood clotting disorder that makes you more likely to get abnormal blood clots, putting you at high risk for deep vein thrombosis (DVT) and pulmonary embolism. It is rare, affecting about 1 in 2,000 to 3,000 people.
Is antithrombin deficiency genetic?
Yes. It is caused by a mutation on the SERPINC1 gene inherited from one of your parents. There is a 50% chance of passing the mutation to each child regardless of sex, and babies inheriting it from both parents usually do not survive.
What are the symptoms of antithrombin deficiency?
The most common symptoms are deep vein thrombosis (DVT) and pulmonary embolism, with your first blood clot usually happening before age 40. Less commonly, clots can form in veins in the brain and abdomen.
How is antithrombin deficiency treated?
After a blood clot, treatment is warfarin (Coumadin), a blood thinner taken for a few months or possibly long-term. People who have the deficiency but have never had a blood clot do not need blood thinners.
Do I need blood thinners if I have antithrombin deficiency but never had a clot?
No. People who have antithrombin deficiency but haven't had a blood clot don't need to take blood thinners.
Is antithrombin deficiency dangerous during pregnancy?
Yes — 3% to 50% of pregnant women with antithrombin deficiency get blood clots. Your provider may give you heparin injections during pregnancy to prevent clots.
How long does antithrombin deficiency last?
It is lifelong. Hereditary antithrombin deficiency is something you're born with and remains part of your genetic makeup for life.
Can antithrombin deficiency be prevented?
You cannot prevent the inherited deficiency itself, since you cannot change the genes you inherited. You can, however, reduce clot risk by avoiding birth control pills and hormone therapy, staying active, not smoking, and maintaining a healthy weight.
References
American Heart Association. A Patient's Guide to Taking Warfarin. heart.org/a-patients-guide-to-taking-warfarin
Genetic and Rare Diseases Information Center. Hereditary antithrombin deficiency. rarediseases.info.nih.gov/diseases/6148/hereditary-antithrombin-deficiency
MedlinePlus. Hereditary antithrombin deficiency. medlineplus.gov/genetics/condition/hereditary-antithrombin-deficiency
National Organization for Rare Disorders. Antithrombin Deficiency. rarediseases.org/rare-diseases/antithrombin-deficiency
Medical Disclaimer: This article is for general informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Only a qualified healthcare provider can diagnose antithrombin deficiency and prescribe blood thinners. If you experience signs of deep vein thrombosis (leg pain, swelling, redness) or pulmonary embolism (sudden chest pain, shortness of breath), seek emergency medical care immediately. If you are taking warfarin and develop a head injury, vomiting blood, or uncontrolled bleeding, go to the emergency room right away.
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