Acquired Antithrombin III Deficiency

Acquired antithrombin III deficiency is a condition where the body doesn’t have enough of a natural blood-thinning protein, putting people at higher risk for dangerous blood clots that can affect the legs, lungs, and other organs.

Table of contents

• What is Acquired Antithrombin III Deficiency?
• How This Condition Develops
• Common Signs and Symptoms
• How Doctors Find This Condition
• Treatment Options
• What to Expect

What is Acquired Antithrombin III Deficiency?

Acquired antithrombin III deficiency is a blood clotting problem where your body doesn’t have enough of a protein called antithrombin (also known as antithrombin III). This protein acts like a brake on your blood clotting system, stopping clots from forming when they shouldn’t. 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 antithrombin needs to stop the clotting before it goes on too long.^[2]

Antithrombin helps keep your blood from clotting excessively. It works by neutralizing the activity of several important clotting factors in your blood, including thrombin (the main clotting enzyme) and other factors called IIa, IXa, and Xa. When your antithrombin isn’t working right or there isn’t enough of it, clotting can keep going without anything stopping it.^[2][3]

How This Condition Develops

Unlike the inherited form of antithrombin deficiency that you’re born with, acquired antithrombin III deficiency develops during your lifetime. It happens primarily because your body is either using up antithrombin too quickly or not producing enough of it.^[3]

Several medical conditions can lead to acquired antithrombin III deficiency. Common situations where this happens include disseminated intravascular coagulation (a serious condition where blood clots form throughout the body), certain blood disorders that damage blood vessels (like hemolytic-uremic syndrome), veno-occlusive disease (especially in patients undergoing bone marrow transplantation), severe infections called sepsis, liver disease, and nephrotic syndrome (a kidney disorder).^[3]

Other causes include the use of oral contraceptives and even treatment with heparin, a blood-thinning medication. Major surgery and cardiopulmonary bypass procedures can also lead to reduced antithrombin levels.^[3][4]

Common Signs and Symptoms

People with acquired antithrombin III deficiency are at high risk for developing abnormal blood clots. The most common problems include deep vein thrombosis (DVT), which is a blood clot in the deep veins of the body, usually in the legs, and pulmonary embolism, which occurs when a clot travels to the lungs.^[2]

Although less common, blood clots can also develop in veins in the brain and abdomen. These clots can be dangerous and require immediate medical attention.^[2]

How Doctors Find This Condition

To diagnose antithrombin III deficiency, your doctor will need to perform several steps. These include a physical examination and taking your medical history to understand any underlying conditions you may have.^[2]

The key test is a blood test that specifically measures the levels of antithrombin in your blood. This test can determine whether you have enough antithrombin or if your levels are too low.^[2]

Your doctor may also order other laboratory tests, including measurements of how long your blood takes to clot, tests for other clotting proteins, and checks for antibodies that can affect clotting. If a blood clot is suspected, imaging tests may be needed. These can include ultrasound of the affected area, chest scans to look for clots in the lungs, or other imaging studies depending on where the clot might be.^[3]

Treatment Options

Treatment for acquired antithrombin III deficiency depends on your specific situation and the underlying cause of the deficiency. The main goal is to prevent new blood clots from forming and to treat any existing clots.^[5]

If you’ve had a blood clot, your doctor may prescribe blood-thinning medications. Warfarin (Coumadin) is commonly used and may be taken for several months or possibly long-term. The medicine works by blocking vitamin K, which your body needs to make clotting factors. Your doctor will need to monitor your blood regularly with a test called prothrombin time (PT) to make sure you’re getting the right dose—not too much that causes bleeding, but enough to prevent dangerous clots.^[2][5]

In some situations, especially during high-risk procedures or in severe cases, doctors may give you antithrombin III replacement therapy using antithrombin III concentrates or fresh frozen plasma. This directly replaces the missing protein in your blood.^[5]

For preventing blood clots, doctors may use a type of medication called low-molecular-weight heparin (LMWH), such as enoxaparin. However, in people with antithrombin III deficiency, these medications don’t work as well as they do in healthy people, so doctors must monitor their effectiveness carefully. Alternative medications like warfarin may be preferred.^[5]

How long you’ll need treatment depends on your situation. For a first blood clot, treatment typically lasts at least 3 to 6 months. If the underlying cause can’t be fixed, or if you have more than one clot, your doctor may recommend continuing blood thinners indefinitely.^[5]

What to Expect

If you have acquired antithrombin III deficiency, it’s important to keep all your appointments with your doctor. Because blood-thinning medications can cause bleeding, your healthcare provider needs to monitor you regularly to ensure you’re getting the right amount of medicine.^[2]

The outlook for people with acquired antithrombin III deficiency depends largely on treating the underlying condition that caused the deficiency in the first place. With proper treatment and monitoring, many people can manage this condition successfully and reduce their risk of dangerous blood clots.