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Antithrombin III Deficiency

Last updated March 11, 2020

Approved by: Maulik P. Purohit MD, MPH

Antithrombin III Deficiency is an uncommon hereditary blood-related disorder causing the formation of clots either in the arteries or veins.

What are the other Names for this Condition? (Also known as/Synonyms)

  • AT 3 Deficiency
  • AT III Deficiency
  • Hereditary Thrombophilia due to Antithrombin III Deficiency

What is Antithrombin III Deficiency? (Definition/Background Information)

  • Antithrombin III Deficiency (AT III Deficiency) is an uncommon hereditary blood-related disorder that arises when the blood becomes too thick, causing the formation of clots either in the arteries or veins of the affected individuals
  • Antithrombin III is a protein produced in the liver, and it helps prevent the formation of clots. In AT III Deficiency disorder, there is insufficient amount of this protein and thus, the body is unable to prevent the formation of (undesirable) clots
  • Antithrombin III Deficiency is an inherited genetic disorder, but it may also be acquired. If the condition is an acquired form, then it is treatable, if proper measures are taken appropriately
  • In some cases, the condition is not identified until very late in life, while in other cases it can be diagnosed quite early, especially if there is a family history of it
  • Individuals with Antithrombin III Deficiency are prone to developing blood clots in their leg veins. The blood clots in the leg veins may travel to the lungs and may cause lung and heart failure
  • Treatment requires keeping the patients on blood thinners and regular follow-up with their primary care physician. AT III Deficiency disorder has good prognosis if appropriate measures are taken

Who gets Antithrombin III Deficiency? (Age and Sex Distribution)

  • Antithrombin III Deficiency is a condition that can be seen during fetal development or during later stages of life. Thus, it can be inherited if it runs in the family, or it may develop due to a new mutation in the gene during the fetal development stage
  • The disorder is equally seen among both genders and can affect any population
  • There is no current study indicating that it is more common in a specific racial or ethnic group

What are the Risk Factors for Antithrombin III Deficiency? (Predisposing Factors)

Risk factors for developing Antithrombin III Deficiency are:

  • Individuals who have a history of this condition are very likely to inherit AT III Deficiency
  • Individuals with particular diseases, such as certain heart conditions, cancers, or kidney and liver functional abnormalities, also have an increased risk for developing this condition

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases ones chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Antithrombin III Deficiency? (Etiology)

  • Antithrombin III Deficiency is an inherited genetic condition; it is present at birth
  • This deficiency disorder can also arise during the fetal stages due to a new mutation in a gene with no prior family history. The mutation can harm the normal function of antithrombin III protein
  • If any member in the family has the disorder, then the remaining (blood-related) family members are at risk for developing the condition and thus, should be tested immediately

What are the Signs and Symptoms of Antithrombin III Deficiency?

Individuals with Antithrombin III Deficiency are at an increased risk of unwarranted blood clot formations. The clots are usually formed in the leg veins (deep venous thrombosis). These individuals may have one leg swollen in comparison to the other leg.

The leg clots can travel to the lungs and cause the following symptoms:

  • Productive cough with bloody sputum
  • Feeling weak and commonly passing-out (fainting)
  • Inability to breath properly
  • Tightness of the chest

How is Antithrombin III Deficiency Diagnosed?

The diagnosis of Antithrombin III Deficiency may include:

  • Antithrombin III Deficiency may be diagnosed through proper family history and physical examination, which will help in evaluating whether or not the individual has the disorder
  • Ultimately, being screened for this condition very early in life, especially when the individual is aware of having a family history for the condition, is the best way to diagnose AT III Deficiency early. Otherwise, unless a clot is formed, the condition remains silent and hidden

Certain diagnostic blood tests include:

  • Test for blood levels of antithrombin III
  • PT (Prothrombin time) and APTT (activated partial thromboplastin time): These tests are good indicators of coagulation status of the body
  • Doppler ultrasound to check leg veins for blood clot formation

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Antithrombin III Deficiency?

The possible complications of Antithrombin III Deficiency are:

  • Formation of blood clots in the leg veins (deep venous thrombosis). The clots formed in the legs can travel to the lungs
  • Lung clots are very dangerous and can cause death if not addressed promptly
  • Heart failure on the right side

How is Antithrombin III Deficiency Treated?

Treatment options for Antithrombin III Deficiency include:

  • Blood thinning medications are given to prevent clot formation
  • Medications, such as warfarin or heparin, are generally administered to thin blood
  • In most cases, the affected individuals are required to have regular follow-up with their healthcare provider in order to monitor the blood thickness. This will also help in determining if adjustments are needed in the drug dosage, or if the medications can be stopped entirely

How can Antithrombin III Deficiency be Prevented?

  • Currently, there are no specific methods or guidelines to prevent Antithrombin III Deficiency, since it is a genetic condition
  • Genetic testing of the expecting parents (and related family members) and prenatal diagnosis (molecular testing of the fetus during pregnancy) may help in understanding the risks better during pregnancy
  • If there is a family history of the condition, then genetic counseling will help assess risks before planning for a child
  • Active research is currently being performed to explore the possibilities for treatment and prevention of inherited and acquired genetic disorders
  • If an individual is diagnosed with the condition, then it is recommended that all members of the family be screened for the presence of Antithrombin III Deficiency disorder

What is the Prognosis of Antithrombin III Deficiency? (Outcomes/Resolutions)

  • The prognosis of Antithrombin III Deficiency is fairly good, if close monitoring of the disorder is maintained
  • In order to have the best outcomes, individuals are required to remain on anticoagulant (blood-thinning) medications

Additional and Relevant Useful Information for Antithrombin III Deficiency:

  • Pregnant women with Antithrombin III Deficiency are not advised to take warfarin
  • If expectant women are on warfarin, they should be stopped immediately, since warfarin is known to cause birth defects in the fetus. Instead, an alternative approach, such as low molecular weight heparin, may be administered, as it does not cross the placenta
  • Antithrombin, a protein formed by the liver, is a natural “blood thinner” that protects the body from excessive or inappropriate blood clotting

The following article link will help you understand antithrombin test:


What are some Useful Resources for Additional Information?

References and Information Sources used for the Article:

Helpful Peer-Reviewed Medical Articles:

Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: June 8, 2015
Last updated: March 11, 2020