How can you self-manage and adjust anticoagulants in the long term?
Some anti-clotting tablets (oral anticoagulants) are used to stop the blood from clotting too quickly. They aim to lower the risk of cardiovascular diseases, especially strokes. They are often prescribed for people who have atrial fibrillation, artificial heart valves or people who have had pulmonary embolism.
Various anticoagulant tablets are available. Vitamin K antagonists are commonly used. They’re also known as coumarins. In Germany, the most frequently used drug from that group is phenprocoumon. It is best known under the trade name Marcumar, but also as Falithrom and Phenprogramma.
Vitamin K antagonists are highly effective medications that considerably decrease the blood's ability to clot. Regular blood clotting monitoring is necessary to make sure that the dosage is correct. If the dosage is correct, the blood doesn’t clot too quickly or too slowly. To prevent blood clots, it must not clot too quickly. But it also must not clot too slowly, because that could easily lead to bleeding.
How is blood coagulation measured?
People who are on vitamin K antagonists usually have their blood checked once a week at first. For this purpose, a blood sample is taken and the INR value (international normalized ratio) is measured. The INR value reflects the blood clotting speed.
The INR value is normally 1. This value is higher in people who are taking anti-clotting medication because it takes longer for their blood to clot. An INR value of “2”, for example, means that the blood takes twice as long to clot. Different people may have different target INR values, depending on their underlying medical condition and risk factors. If the INR value hardly changes over several consecutive weeks, the blood tests can be done less frequently. If the target value is achieved over several months, it’s enough to then only check the values every four to six weeks.
The target INR range for people with atrial fibrillation is generally between 2 and 3. If the value is higher, for example 3.5, the drug dose is reduced. If it is lower, for example 1.5, the dose is increased a bit. This medication does not work immediately, so it generally takes a few days for the INR value to change.
How can I check my blood myself?
It is not absolutely necessary to always go to the doctor to have your blood tested. You can take a training course to learn how to measure your INR values on your own. To monitor your blood values yourself you simply have to prick your finger and smear a drop of blood onto a test strip. The test strip is then inserted into a special device that measures the INR value. Some people also adjust their dose themselves. People who monitor their own blood values only have to go to the doctor's every couple of months.
Self-monitoring training courses do not only teach how to monitor your own blood values and adjust your medication. They also provide important information about many other treatment aspects like how your diet can influence your blood's clotting speed, interactions with other medications, and what you have to bear in mind if you are having an operation and take anticoagulants.
Many people who take anticoagulants find that self-monitoring has advantages because it means that they are more flexible and more independent. Studies have also shown that people who monitor their own values are better able to control them and more rarely develop blood clots that lead to complications.
Dantas GC, Thompson BV, Manson JA, Tracy CS, Upshur RE. Patients' perspectives on taking warfarin: qualitative study in family practice. BMC Fam Pract 2004; 5: 15.
Heneghan C, Ward A, Perera R, Bankhead C, Fuller A, Stevens R et al. Self-monitoring of oral anticoagulation: systematic review and meta-analysis of individual patient data. Lancet 2012; 379(9813): 322-334.
Kasper DL, Fauci AS, Hauser SL, Longo DL, Jameson JL, Loscalzo J. Harrison's Principles of internal medicine. New York: McGraw Hill; 2015.
Mutschler E, Geisslinger G, Menzel S, Ruth P, Schmidtko A. Pharmakologie kompakt: Allgemeine und Klinische Pharmakologie, Toxikologie. Stuttgart: Wissenschaftliche Verlagsgesellschaft; 2016.
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