Anticoagulant medications

How coagulation levels remain steady

Dr. Jens Heidrich, MD, explains why some people need an anticoagulant and introduces the concept of self-testing, which empowers patients to keep an eye on their coagulation levels by themselves

When does one need to take anticoagulant medications?

Following the implantation of an artificial heart valve, the body reacts with increased blood coagulability. This may produce a blood clot, or thrombus. This is also a risk in atrial fibrillation because here the blood flow is either irregular or too slow, as well as in blood clotting disorders. In order to prevent all this, anticoagulants, also known as blood thinners, are used.

How do anticoagulant medications work?

There are a number of different groups of anticoagulant medications. The so-called vitamin K antagonists 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. Nowadays, there are also direct oral anticoagulants (DOACs), which according to current opinion, no longer need a check of the coagulation value.

How do you measure the level of anticoagulation?

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 on the patient most 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 so-called INR level.

What does INR mean?

INR stands for international normalized ratio. This worldwide unit indicates to what extent blood clotting is slowed. In a patient with an INR of two, it takes twice as long for the blood to clot compared with a person who is not taking an anticoagulant. INR testing to monitor treatment is usually performed by a family doctor, but it is also possible for patients to measure their INR themselves, which has many advantages.

With self-testing, the patient gains more confidence in the treatment and loses the fear of suffering bleeding and thromboses.

Common conditions

Atrial fibrillation

When the heart gets out of rhythm


When clots become dangerous

Mechanical heart valve

When the heart needs support

Frequently asked questions

Blood coagulation is vital, because without it you would not stop bleeding after an injury. The thickening and clotting of blood is a complex process involving numerous substances produced by the body (e.g., clotting factors and platelets). Coagulation involves three important steps:

  • The vascular walls at the place of the injury contract.
  • The blood platelets stick together and form a blood clot that seals the place of the injury.
  • Coagulation factors are formed in the liver that ensure that the blood clot solidifies and does not dissolve.

In healthy people, coagulation works reliably and potentially dangerous clots are not formed. In other words: the system is in balance.

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. The following are the main types of anticoagulants:

  • Vitamin K antagonists, also known as Coumadin (or warfarin)
  • Heparin
  • Thrombocyte aggregation inhibitors
  • DOACs (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. For some patients, regular self-testing of their INR levels may be of great benefit.

When taking vitamin K antagonists, 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 doctor determines the therapeutic range in which your coagulation level should be.

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).

The Quick value is also a commonly used unit but has become less popular than INR because it can fluctuate greatly. The Quick value is stated as a percentage (normal range: 70–130%) and is opposite to the INR in that a high percentage is equivalent to a low INR, and vice versa.

Based on what you’re being prescribed anticoagulants for, your doctor 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.

Recommended ranges:

  • Atrial fibrillation: INR of 2.0–3.0.
  • Heart valve replacement: INR of 2.0–3.5. This depends on the type of heart valve used and whether the heart rhythm is regular.
  • Thrombosis or lung embolism: INR of 2.0–3.0.

These are recommended ranges only. Your doctor will determine what your target INR range is.

INR monitoring is done in your doctor’s office at regular intervals, as your doctor 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. For more information, please see the Self-testing section.

If you are receiving ongoing anticoagulant therapy with vitamin K antagonists, there are a few things you should watch out for. For instance, do your best to avoid injuries and cuts because this could lead to increased bleeding. There are also some nutritional and travel considerations to keep in mind — but not to the point where it should interfere with your enjoyment of daily life. Read stories of how people manage their anticoagulant therapy while remaining independent and living life to the fullest here.

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