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Understanding anticoagulation

What you need to know about anticoagulant medications.

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Anticoagulant medication is a common part of treatment for some conditions

Atrial fibrillation (AF) is a disorder of the heart rhythm.

In the heart of a person with AF, the heart quivers, or fibrillates, rapidly and irregularly rather than beating effectively. This leads to symptoms such as palpitations and shortness of breath. It also means that blood flow within the heart itself can become sluggish and there is a risk of clot formation on the walls lining the heart, especially within the chamber known as the atrium. This can lead to a heart attack.

Anticoagulants lengthen the time it takes for blood to clot, and therefore reduce the risk of a clot developing.

Deep vein thrombosis (DVT) occurs when a blood clot forms in a vein. It usually develops in the calf muscle, less frequently in the thigh, and sometimes in other deep-lying veins in the body.

Some of the common symptoms of a DVT are:

  • Tenderness in the leg
  • Redness
  • Swelling and a feeling of tightness—the skin may feel “stretched”
  • Pain

However, some DVTs have no symptoms at all.

There may be increased risk of DVT under conditions of:

  • Prolonged immobility (e.g., long journeys where you sit still without being able to stretch your legs or move about)
  • A medical condition that restricts normal movement or activity
  • Surgery, such as orthopaedic surgery or illness, that requires treatment such as chemotherapy
  • Genetic or inherited conditions
  • Existing vein damage from a previous DVT
  • The contraceptive pill and hormone replacement therapy
  • Pregnancy

Some people may only realize they have a DVT when they experience a pulmonary embolism.

A pulmonary embolism (PE) is a blood clot in the lung that usually originates from smaller blood vessels in the leg. A clot from a DVT travels to the lungs and through the vessels of the lung until it reaches smaller vessels where it becomes lodged. The clot then prevents any further blood from travelling to that section of the lung, which can eventually lead to stroke.

Common symptoms of PE may include:

  • Chest pain that is sharp and is worse when taking a deep breath
  • Shortness of breath
  • Low blood pressure
  • Sweating
  • Anxiety

All the above can also be symptoms of other conditions; however, a PE can be life threatening, so if you are concerned, seek the advice of a doctor or go to your nearest emergency department.

People who experience a PE may be in hospital for several days until their anticoagulant medication is introduced and stabilized. They may remain on anticoagulation therapy for six months or longer.

Modern heart surgery has transformed the lives of many people who were either were born with damaged heart valves or developed them as they grew older. When heart valves are damaged, the problem is either that the valve is narrow or that it no longer fully closes.

They can now be replaced with either a biological valve (e.g., a pig heart valve treated for use in humans) or a mechanical valve made out of synthetic material. Mechanical heart valves are more durable; however, there is an increased risk of clot formation. To reduce the risk of clotting, your doctor may prescribe an oral anticoagulant.

There are different kinds of anticoagulant medications

There are a number of types of anticoagulant medications, also known as blood thinners. The medical term for these is oral anticoagulants.

When they are ingested, the natural clotting of the blood is reduced and it takes longer for it to clot. There are four main types of anticoagulants:

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Vitamin K antagonists,

also known as Coumadin (or warfarin)

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Thrombocyte aggregation inhibitors

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(also known as thrombin and factor Xa inhibitors)

For long-term or ongoing anticoagulant therapy, vitamin K antagonists or DOACs can be used. Both are taken as tablets. Vitamin K antagonists are the most common because they have been used for over 60 years, and doctors are familiar with their effects and safety profile.

A major advantage of using vitamin K antagonists is patient self-testing of coagulation (INR levels). Self-testing of coagulation levels is not possible with DOACs (direct oral anticoagulants). For some patients, regular self-testing of their INR levels may be of great benefit.

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How anticoagulants work in the body

There are a number of different groups of anticoagulant medications, though vitamin K antagonists (VKAs) are often used. Their name derives from their mode of action, since they are counterparts of vitamin K, which is absorbed from food and is formed by our intestinal bacteria. Vitamin K is very important for blood coagulation. If vitamin K inhibitors are taken, the blood clots more slowly and the risk of thrombosis is reduced (this is where we get the term “blood thinner” from).

How you measure the level of anticoagulation

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In order to monitor anticoagulant therapy with vitamin K antagonists, blood is taken from the vein or fingertip. The time it takes for the blood to clot can be measured in the lab with a coagulometer. However, the coagulation level can also be measured directly by the patient very reliably with a small, mobile measuring device. Patients can even check their coagulation level at home at any time. The result is displayed as the INR level.

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INR stands for international normalized ratio. It is the most common method of measuring to what extent the blood clotting is slowed. For instance, in a patient with an INR of 2.0, it takes twice as long for the blood to clot compared with a person who is not taking an anticoagulant (and has an INR of 1.0).

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INR monitoring can be done in your doctor’s office or in pharmacies at regular intervals, as your healthcare provider sees best. With self-testing, weekly monitoring is recommended. Studies have shown that patient self-testing is associated with significantly more values within the therapeutic range than is testing carried out in the doctor’s office.

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Why it is important to measure anticoagulation levels

When taking vitamin K antagonists, such as warfarin, the coagulation level needs to be monitored regularly in order to check whether the optimal dose is being used. If the dose is too low, a clot may form. If it is too high, there is a risk of bleeding. It is important to balance these two risks. To do this, your healthcare provider determines the therapeutic range in which your coagulation level should be.

Based on the reason you have been prescribed anticoagulants, your healthcare provider will determine an individualized therapeutic INR range. This is the target range: your INR should not be higher or lower, as this may increase the risk of bleeding or a clot.

Do you have other questions about anticoagulation medications?

Visit our FAQ page for answers.

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