Blood Clot Formation
When you cut or injure yourself, your body stops the bleeding by forming a blood clot. Proteins and particles in your blood, called platelets, stick together to form the blood clot. The process of forming a clot is called coagulation. Normal coagulation is important during an injury, as it helps stop a cut from bleeding and starts the healing process.
However, the blood shouldn’t clot when it’s just moving through the body. If blood tends to clot too much, it is referred to as a hypercoagulable state or thrombophilia.
Are hypercoagulable states dangerous?
Hypercoagulable states can be dangerous, especially when these conditions are not properly identified and treated. People with hypercoagulable states have an increased risk for blood clots developing in the arteries (blood vessels that carry blood away from the heart) and veins (blood vessels that carry blood to the heart). A clot inside a blood vessel is also called a thrombus or an embolus.
Blood clots in the veins or venous system can travel through the bloodstream and cause deep vein thrombosis (a blood clot in the veins of the pelvis, leg, arm, liver, intestines or kidneys) or a pulmonary embolus (blood clot in the lungs).
Blood clots in the arteries can increase the risk for stroke, heart attack, severe leg pain, difficulty walking, or even the loss of a limb.
What causes hypercoagulable states?
Hypercoagulable states are usually genetic (inherited) or acquired conditions. The genetic form of this disorder means a person is born with the tendency to form blood clots. Acquired conditions are usually a result of surgery, trauma, medications or a medical condition that increases the risk of hypercoagulable states.
Inherited hypercoagulable conditions include:
- Factor V Leiden (the most common)
- Prothrombin gene mutation
- Deficiencies of natural proteins that prevent clotting (such as antithrombin, protein C and protein S)
- Elevated levels of homocysteine
- Elevated levels of fibrinogen or dysfunctional fibrinogen (dysfibrinogenemia)
- Elevated levels of factor VIII (still being investigated as an inherited condition) and other factors including factor IX and XI
- Abnormal fibrinolytic system, including hypoplasminogenemia, dysplasminogenemia and elevation in levels of plasminogen activator inhibitor (PAI-1 )
Acquired hypercoagulable conditions include:
- Some medications used to treat cancer, such as tamoxifen, bevacizumab, thalidomide and lenalidomide
- Recent trauma or surgery
- Central venous catheter placement
- Supplemental estrogen use, including oral contraceptive pills (birth control pills)
- Hormone replacement therapy
- Prolonged bed rest or immobility
- Heart attack, congestive heart failure, stroke and other illnesses that lead to decreased activity
- Heparin-induced thrombocytopenia (decreased platelets in the blood due to heparin or low molecular weight heparin preparations)
- Lengthy airplane travel, also known as "economy class syndrome"
- Antiphospholipid antibody syndrome
- Previous history of deep vein thrombosis or pulmonary embolism
- Myeloproliferative disorders such as polycythemia vera or essential thrombocytosis
- Paroxysmal nocturnal hemoglobinuria
- Inflammatory bowel syndrome
- Nephrotic syndrome (too much protein in the urine)
How is a hypercoagulable state diagnosed?
Careful Medical History
Certain conditions increase a person’s risk for developing blood clots, but do not necessarily indicate a genetic hypercoagulable state. Therefore, a careful evaluation of the patient’s personal and family medical history is needed.
Patients may be candidates for screening for hypercoagulable states if they have:
- A family history of abnormal blood clotting
- Abnormal blood clotting at a young age (less than age 50)
- Thrombosis in unusual locations or sites, such as veins in the arms, liver (portal), intestines (mesenteric), kidney (renal) or brain (cerebral)
- Blood clots that occur without a clear cause (idiopathic)
- Blood clots that recur
- A history of frequent miscarriages
- Stroke at a young age
If you have one of the previously listed conditions, your doctor may recommend blood tests to further evaluate your condition.
These tests should be performed at a specialized coagulation laboratory and interpreted by a pathologist or clinician with expertise in coagulation, vascular medicine or hematology.
Ideally, the tests should be done when you are not having an acute clotting event.
The most common lab tests include:
- PT-INR: The prothrombin time (PT or protime) test is used to calculate your International Normalized Ratio (INR). The information is used to monitor your condition if you are taking warfarin (Coumadin). Your INR will help your healthcare provider determine how fast your blood is clotting and whether your warfarin (Coumadin) dose needs to be changed.
- Activated partial thromboplastin time (aPTT): Measures the time it takes blood to clot. This test is used to monitor your condition if you are taking heparin.
- Fibrinogen level
- Complete blood count (CBC)
Some of the tests help detect the antiphospholipid antibody syndrome or dysfibrinogenemias- conditions that can be associated with hypercoagulable states.
Tests used to help diagnose inherited hypercoagulable states include:
- Genetic tests, including factor V Leiden (Activated protein C resistance) and prothrombin gene mutation (G20210A)*
- Antithrombin activity
- Protein C activity
- Protein S activity**
- Fasting plasma homocysteine levels
* Factor V Leiden and prothrombin gene mutation (G20210A) are the most commonly identified genetic defects that increase a person’s risk for blood clotting.
** Additional lab tests, such as measurement of free (active) and total protein S antigen levels, may be required in order to validate protein S activity assay results.
Other tests used to help diagnose acquired hypercoagulable states include tests for:
- Anticardiolipin antibodies (ACA) or beta-2 glycoproteins, which are part of the antiphospholipid antibody syndrome*
- Lupus anticoagulants (LA), part of the antiphospholipid antibody syndrome*
- Heparin antibodies (in patients who develop low platelet counts while exposed to heparin)
*The presence of antiphospholipid antibodies (ACA) and a lupus anticoagulant (LA) is important when evaluating someone who has had recurrent miscarriages and venous or arterial thrombosis.
Testing helps identify whether the patient is at risk for further clotting and helps determine an appropriate course and length of treatment to prevent future clots. Testing also may help to identify relatives who don’t currently have symptoms but may be at risk.
How are hypercoagulable states treated?
In most cases, treatment is only needed when a blood clot develops in a vein or artery. Anticoagulants decrease the blood’s ability to clot and prevent the formation of additional clots.
Anticoagulant medications include:
- Warfarin (Coumadin) comes in tablet form and is taken orally (by mouth).
- Heparin is a liquid medication and is given either through an intravenous (IV) line that delivers the medication directly into the vein, or by subcutaneous (under the skin) injections given in the hospital.
- Low-molecular weight heparin is injected subcutaneously once or twice a day and can be taken at home.
- Fondaparinux (Arixtra) is injected subcutaneously.
You and your family will be instructed on how to take the anticoagulant medication that is prescribed.
Your doctor will talk to you about the benefits and risks of these medications. This information, along with your diagnosis, will help determine the type of anticoagulant medication you will take, how long you will need to take it, and the type of follow-up monitoring you need.
As with any medication, it is important to know how and when to take your anticoagulant according to your doctor’s guidelines, and to have frequent blood tests, as ordered by your doctor.
If you're prescribed warfarin (Coumadin):
- You will need to have frequent blood tests, called the PT-INR, to evaluate how well the medication is working. Please keep all scheduled lab appointments so your response to the medication can be monitored. Your medications may be changed or adjusted based on the results of this test.
- You should order and wear a medical identification bracelet so you can receive proper medical care in case of an emergency situation.
- You may bleed or bruise more easily when you are injured. Call your doctor if you experience heavy or unusual bleeding or bruising.
- Certain nonprescription (over-the-counter) medications affect how anticoagulants work. Do not take any other medications without first talking to your doctor.
- Ask your doctor about specific dietary guidelines you'll need to follow while taking warfarin. Certain foods, such as foods high in vitamin K (found in brussel sprouts, spinach and broccoli) can change the way the medication works.
- You should not take warfarin (Coumadin) if you're pregnant or planning to become pregnant. If you are, ask your doctor about switching to a different type of anticoagulant medication.
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Choosing a doctor to treat your vascular disease depends on where you are in your diagnosis and treatment. The following Heart and Vascular Institute Sections and Departments treat patients with all types of vascular disease, including blood clotting disorders:
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