Antithrombin III Deficiency

Antithrombin III deficiency (also known as ATIII deficiency) is a type of clotting disorder in which blood gets abnormally clotted in blood vessels. It was in the year 1965 when Antithrombin III was first described.1

Antithrombin iii deficiency

How common is Antithrombin III deficiency?

Antithrombin deficiency is observed in 0.02 to 1.1% of the total population. In the patients of venous thromboembolism, this disorder has a 4% chance of being present1. In the United States, Antithrombin III deficiency occurs 1 in 1000 people2

Causes of Antithrombin III Deficiency

Antithrombin III is just a kind of protein in your blood. Its function is to naturally block the formation of abnormal blood clots. It keeps a healthy between bleeding and clotting.

The congenital Antithrombin III deficiency occurs when a person receives one abnormal copy of the Antithrombin III gene from a parent with the disease.

The abnormal gene leads to low levels of Antithrombin III. These low levels of Antithrombin III can cause abnormal blood clots (thrombi) that can block blood flow and damage organs.

People with congenital Antithrombin III deficiency are likely to get a blood clot at very young age. They also might be having family members who have had a problem of blood clotting.3

Types of ATIII deficiency

Antithrombin III deficiency can be:

  • Inherited: Present at birth (or Congenital) from parents to the child.
  • Acquired: Present after birth and can occur in:
    • Neonates
    • Pregnancy
    • Liver disease
    • Kidney disease
    • Bone marrow transplantation
    • Sepsis (infection spread in blood)
    • Drug-induced reduction in Antithrombin levels

The Genetics behind Antithrombin III deficiency simplified:

A specific gene responsible for production of Antithrombin III is passed onto you from your parents. In fact two normal copies of this gene – one from mother, another from your father are normally passed onto you. In case of inherited Antithrombin III deficiency, either one abnormal gene & one normal gene or two abnormal Antithrombin III genes are passed onto you. On this basis, the patients are divided into two groups:

  • Heterozygous Antithrombin III deficiency: The person, who has 1 defective Antithrombin III deficiency inherited either from father or mother, is known as heterozygous for Antithrombin III deficiency.
  • Homozygous Antithrombin III deficiency: The person, who has 2 defected Antithrombin III genes – one defective gene from father and other defective gene from mother, is known as homozygous for Antithrombin III deficiency.

Two primary types of the Antithrombin III deficiency exist:

  • Type I Antithrombin deficiency: It is characterized by an insufficient quantity of normal Antithrombin present. The Antithrombin to inactivate the coagulation factors is not simply enough.
  • Type II Antithrombin deficiency: There is normal quantity of Antithrombin present in the blood. However, this amount is simply not able to execute function properly.1

Symptoms of Antithrombin III Deficiency

Patients suffering from Antithrombin III deficiency have the symptoms of blood clots. These include:

  • Coughing up blood
  • Shortness of breath
  • Fainting
  • Chest pain when asked to take deep breaths
  • Swelling of one of the legs3

Other less common findings include:

  • Neurological symptoms like headaches
  • Rash
  • Cardiovascular disease
  • Bleeding3

Diagnosing Antithrombin III Deficiency

A blood test is used to measure the amount of Antithrombin protein in your blood. There specialized laboratories for performing these kinds of tests. You cannot be tested for Antithrombin deficiency in case you are taking the anticoagulant heparin (or low-molecular weight heparin).2

Treatment for Antithrombin III Deficiency

When the patient with Antithrombin III deficiency has a venous clot, that person will have to receive anticoagulation. The drugs used include the anticoagulants like:

  • Heparin
  • Low-molecular-weight heparins
  • Warfarin

These medications are generally used for 3-6 months.

In case of patients who have had many episodes of abnormal blood clots, or are at increased risk of having further such episodes, they are considered for a long-term management on an oral anticoagulant (Warfarin).

Antithrombin concentrates can also be used for managing this deficiency. However, their use is limited to the conditions preventing the use of oral anticoagulant medications. Two such important conditions include:

  • Patient has to undergo a major surgery (as he/she has to stop taking anything orally)
  • Patient is pregnant (Oral anticoagulants like Warfarin are harmful for fetus)1

Pregnancy and Antithrombin Deficiency

As mentioned above, the use of oral anticoagulant Warfarin is never recommended when the patient is a pregnant woman.

Alternatively, the anticoagulation can be done in such patients with heparin or even low-molecular-weight heparins. Also, the patient can be put on Antithrombin concentrate as mentioned above.1

If Antithrombin III Deficiency is left untreated

In case of patients who are homozygous for type II Antithrombin deficiency, there occur severe episodes of venous thrombosis. Arterial thrombus formation has also been reported in such patients.

The patients who are homozygous for type I Antithrombin deficiency are completely incompatible with life. This leads to the death of the fetus inside the mother’s womb.

In heterozygous Antithrombin deficiency, there have been reports of arterial thrombus formation. So, the most important step to be taken for preventing the arterial disease is to control other risk factors. These include:

Prognosis for people with Antithrombin III Deficiency

In case the patients stay on anticoagulant medications, they are expected to have a good outcome.3

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