Antithrombin III: The key "guardian" of the human anticoagulation system

Antithrombin III: The key "guardian" of the human anticoagulation system

In the complex physiological mechanism of the human body, antithrombin III (ATⅢ) plays a vital role. It is one of the most important anticoagulants in our body, silently guarding our blood vessel health and maintaining the normal flow of blood. Today, let us take a deeper look at this "guardian" of the anticoagulation system.
What is antithrombin III?

Antithrombin III is a glycoprotein secreted by hepatocytes with a relative molecular weight of about 58.2 kD, and is a serine protease inhibitor. It maintains the body's blood coagulation balance by inhibiting the activity of thrombin and activated coagulation factors VII, IX, X, XI and XII serine proteases. The role of antithrombin III accounts for about 70% of the total activity of the anticoagulation system and is one of the core components of the human anticoagulation mechanism.
Anticoagulation mechanism of antithrombin III

The anticoagulant effect of antithrombin III is mainly achieved by binding to serine proteases such as thrombin. It can form a 1:1 complex with these enzymes, thereby inhibiting their activity and preventing excessive blood coagulation. This process is like installing a "brake" on the "coagulation switch" in the blood, ensuring that the blood flows smoothly in the blood vessels without forming dangerous thrombi.
It is particularly worth mentioning that heparin can significantly enhance the anticoagulant effect of antithrombin III. Heparin is a polysaccharide substance that is widely present in human tissues. When heparin binds to antithrombin III, it induces a conformational change in antithrombin III, making it easier to bind to thrombin, thereby greatly improving the anticoagulant effect. This mechanism is widely used in clinical anticoagulant therapy, such as in cardiac surgery, hemodialysis and other scenarios where blood coagulation needs to be prevented.
Detection and clinical significance of antithrombin III
Detection principle

The detection of antithrombin III usually adopts the chromogenic substrate method. The principle of this method is to add an excess of thrombin to the plasma to be tested, and thrombin forms a 1:1 complex with antithrombin III in the plasma. The remaining thrombin will act on the chromogenic peptide to cleave the chromogenic group. The degree of color development is positively correlated with the amount of remaining thrombin and negatively correlated with the amount of plasma antithrombin III. In this way, doctors can accurately measure the activity level of antithrombin III in the patient's plasma.
Clinical significance

The change in the level of antithrombin III has important diagnostic and therapeutic significance in clinical practice.
Physiological changes
Infants: Infants under 6 months old have low levels of antithrombin III, which is a normal physiological phenomenon.
Pregnancy: After 13 weeks of pregnancy and in the postpartum stage, the level of antithrombin III will drop significantly, which is to adapt to the physiological changes during pregnancy.
Gender differences: The average level of antithrombin III in premenopausal women is lower than that in men, which is related to hormone levels.
Pathological changes
Pathological increase: Increased antithrombin III levels are common in acute bleeding diseases such as hemophilia, leukemia, aplastic anemia, and in the treatment of oral anticoagulants. In anticoagulant therapy, if heparin resistance is suspected, it can be determined by antithrombin III activity testing. During antithrombin replacement therapy, antithrombin III testing should also be the first choice for monitoring.
Pathological reduction:
Hereditary antithrombin III deficiency: This is an autosomal dominant genetic disease, which is mainly manifested as venous thrombosis (VTE). Patients often develop venous thrombosis after surgery, trauma, infection, pregnancy or postpartum, and thrombosis may occur repeatedly. The incidence of this hereditary deficiency is 0.02% in the population and 1% - 8% in patients with first deep vein thrombosis.
Acquired antithrombin III deficiency:
Synthesis disorder: Severe liver diseases, such as cirrhosis, severe hepatitis, and advanced liver cancer, can lead to antithrombin III synthesis disorder, which is often related to the severity of the disease and may be accompanied by thrombosis.
Excessive consumption: Antithrombin III will be over-consumed in cases of disseminated intravascular coagulation (DIC), venous thrombosis, etc.
Excessive loss: Diseases such as nephrotic syndrome can lead to excessive loss of antithrombin III.
Heparin therapy monitoring

In heparin therapy, the role of antithrombin III is crucial. After heparin binds to antithrombin III, the anticoagulant activity of antithrombin III can increase thousands of times. Heparin mainly exerts an indirect anticoagulant effect by enhancing the activity of antithrombin III. The speed at which antithrombin III inactivates serine protease activity depends on heparin, but the amount of serine protease inactivation depends on the activity of antithrombin III.
AT activity <70%: heparin anticoagulant effect is reduced.
AT activity <50%: heparin anticoagulant effect is significantly reduced.
AT activity <30%: heparin anticoagulation is ineffective.

Therefore, it is very important to monitor the activity level of antithrombin III when using heparin for anticoagulant therapy. By regularly testing antithrombin III, doctors can adjust the dose of heparin in time to ensure the effectiveness and safety of anticoagulant therapy.

Conclusion

Antithrombin III is the key "guardian" of the human anticoagulant system. It plays an important role in maintaining normal blood flow and preventing thrombosis. Understanding the function, detection method and clinical significance of antithrombin III will help us better understand and manage blood diseases. If you or your family members have related symptoms or diseases, it is recommended to seek medical attention in time for professional testing and treatment.