What is it?
A hypercoagulable disorder is an inherited or acquired condition that increases the risk of inappropriate or excessive thrombus (blood clot) formation. Clotting is a normal response to blood vessel or tissue injury. When a blood vessel is injured, it begins to leak blood, either externally or into body tissues. The body stops this blood loss through a complex clotting process called haemostasis. During haemostasis, the injured blood vessel constricts to reduce blood flow, platelets adhere to the injury site and clump together to form a loose platelet plug and the coagulation cascade is initiated. During the cascade process, the body sequentially activates coagulation factors, proteins that create a net of fibrin threads, weave them through the platelet plug and stabilise the resulting blood clot. This clot functions as a barrier to further blood loss, one that stays in place until the injury has healed.
Usually, the body activates the clotting process, regulates its speed and volume with feedback mechanisms, and after the site has healed, breaks down the clot and removes it. Hypercoagulable disorders occur when something goes wrong with the clotting process. If the process activates inappropriately, does not self regulate properly, or resists being broken down, then there can be inappropriate and/or excessive blood clot formation. Blood clots are referred to as thrombi (one – thrombus) when they form in a blood vessel; thrombi may break off and block another blood vessel in another part of the body, where they are referred to as emboli (one – embolus). Thrombi most commonly form in the deep veins of the lower legs (deep venous thrombosis, or DVT), where they may cause pain and swelling. They may also form in arteries and cause heart attacks or strokes. Emboli may involve the brain, where they can cause strokes, or lungs (pulmonary emboli), where they can cause chest pain and shortness of breath.
Certain inherited gene mutations that may predispose someone to hypercoagulable states, such as factor V Leiden or the prothrombin G20210A mutation, are relatively common in the population, but it is thought that they add only a slight increase in the risk of actually developing a problem with clotting. Other inherited hypercoagulable disorders, such as protein C deficiency, protein S deficiency, and antithrombin deficiency, are relatively rare and are usually due to genetic mutations that lead to a deficiency or dysfunction in the coagulation protein that the gene produces. All of the inherited disorders (except for antithrombin deficiency) may be seen in heterozygous (one gene copy) or homozygous (two gene copies) form. If someone has two mutated gene copies, they tend to have a more severe form of the condition, and if they are heterozygous in more than one condition, the risk of clotting tends to be additive (and sometimes they multiply the risk). With inherited hypercoagulable disorders, the first thrombotic episode may be seen at a relatively young age (less than 40 years of age). The patient may have recurrent thrombosis, a family history of thrombosis, and blood clots in unusual sites (such as cerebral veins, hepatic veins, and renal veins).
Acquired disorders are more commonly known to be the cause of hypercoagulable states than inherited ones. They may be related to antiphospholipid antibodies, liver disease, or to some cancers. Disseminated intravascular coagulation (DIC) is a life-threatening, acute, acquired condition that causes tiny clots throughout the body. It uses up coagulation factors at an accelerated rate, leading to both bleeding and inappropriate clotting. The next few pages describe several hypercoagulable disorders.