Antithrombin – when to check its activity and concentration?

Proven content

Antithrombin is an antigen synthesized mainly in the liver and endothelium of blood vessels, megakaryocytes and platelets. In a healthy human, plasma is from 20 to 29 IU / ml with an activity of 75-150%. Antithrombin is the main inhibitor of plasma thrombin and is therefore used to assess the state of the coagulation system.

Antithrombin reduces blood clotting. The level of antithrombin is determined when a doctor wants to exclude one of the causes of hypercoagulability, i.e. its deficiency. After receiving the result, always show it to the doctor. Under what circumstances should antithrombin III tests be performed?

What is antithrombin and how does it work?

Antithrombin III is a glycoprotein antigen. It is found in the blood plasma and its task is to suppress the action of thrombin, which slows down or lengthens the clotting time of the blood. Together with thrombin, it forms a 1: 1 complex. It is then removed from the blood by macrophages. Heparin is an element accelerating the rate of binding of antithrombin III with thrombin and coagulation factors. Therefore, the main function of antithrombin is to inhibit the coagulation system.

Antithrombin III is synthesized in the liver, platelets, megakaryocytes and the endothelium of blood vessels and is the most important thrombin inhibitor. It is important because it not only has anticoagulant but also anti-inflammatory properties.

It is also part of the treatment of diseases resulting from its deficiency. Antithrombin deficiency increases the risk of thromboembolism and thrombosis of the veins of the legs and pelvis.

Venous thrombosis: What should I know about this disease?

What do antithrombin III deficiencies lead to?

Acquired antithrombin III deficiencies may arise under certain circumstances. Deficiencies occur, for example, in the case of:

1. greater consumption of AT III antigen (antithrombin III) in DIC;
2. extensive burns;
3. post-operational period;
4. sepsis;
5. neoplastic diseases;
6. vascular thrombosis;
7. heavy blood loss;
8. nephrotic syndrome;
9. kidney failure;
10. pulmonary embolism;
11. patients after dialysis, plasmapheresis and extracorporeal circulation;
12. liver damage as a consequence of inflammation, fatty degeneration, poisoning or cirrhosis;
13. long-term estrogen therapy.

In some cases, there is only a decrease in the activity of antithrombin III (its concentration remains unchanged). The reverse is also possible.

Blood tests: How do I read the results?

How should you prepare for the test?

Antithrombin III concentration is tested on a blood sample, usually taken from a vein in the arm. The taken sample is sent for analysis. The patient should be fasting.

How is antithrombin III testing done?

The blood to be tested is collected in a test tube containing 3,8% sodium citrate, because the material to be tested is citrate plasma. A blood sample is taken from a vein, most often in the ulna. During the test, the activity of antithrombin III is usually measured, not its concentration. If the values ​​are lowered, your doctor will order antithrombin III antigen testing. If deficiencies are found, the level of activity and the level of antithrombin antigen in the serum should be determined.

Antithrombin III activity is tested by immunological methods. It assesses the tendency to the appearance of blood clots.

What are the types of antithrombin deficiency?

Antithrombin III deficiency can take two forms. Type I means reduced activity and a low level of AT III, i.e. less antithrombin is released, which additionally does not work properly. On the other hand, type II means reduced AT III activity, but the protein values ​​are normal. This means that adequate amounts of protein are secreted, but it is not working properly.

Read: What does a hematologist do?

What are the indications for the test?

Antithrombin III activity is checked together with other tests that your doctor may order for hypercoagulability, especially when you have recurrent thrombotic events. The result depends on both the existing clots and the treatment of the existing clots.

Antithrombin levels are also ordered when the patient does not respond properly to anticoagulant treatment with heparin and is therefore given in higher than usual doses. The problem of antithrombin deficiency may indicate heparin resistance, which is related to the antithrombin-dependent antithrombotic effect of heparin.

When performing antithrombin tests, the doctor first orders an assessment of antithrombin activity, as activity is decreased in all types. This test is used as a screening test. When activity is found to be low, your doctor will usually measure the amount of antithrombin III.

If, with reduced activity, there is also a low protein concentration, it means that we are dealing with type I deficiency. It results from the fact that less antithrombin is involved in the clotting regulation process.

When diagnosed with the second type of deficiency, adequate levels of antithrombin are secreted, but not working properly.

What are the antithrombin norms?

Normal values ​​of antithrombin III are determined within the limits of:

1. 0,19-0.31 g / l – for quantity;
2. 80-120% – for activity.

In any case, show the test results to the doctor.

What if the blood clots too much? Check!

What might the decreased activity of antithrombin III mean?

The decreased activity of antithrombin III may mean, among others:

1. inherited deficiency of antithrombin III;
2. heparin treatment longer than 3 days;
3. chronic liver diseases;
4. acute phase reactions;
5. last trimester of pregnancy;
6. nephrotic syndrome;
7. treatment with asparaginase;
8. acute leukemia;
9. large blood loss;
10. gram-negative sepsis;
11. operations.

The condition is also seen in newborns and women using oral contraception.

Do you need interpretation of test results? Are you worried about your symptoms? Contact your doctor. Make an online teleconsultation with your family doctor at haloDoctor.pl to get answers to your questions.

What might increased antithrombin III activity mean?

Antithrombin may also be higher than the norm. This condition means that the patient:

1. is treated with heparin;
2. has elevated ESR;
3. has hyperglobulinemia;
4. has hepatitis;
5. has a low level of vitamin K.

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