Tuesday, 30. of September 2014
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What happens if the INR is below your therapeutic range?

In her recently published editorial in Thrombosis and Haemostasis 2009; 101:417-418, Prof. Elaine Hylek, MD (Boston, MA) is dealing with this question more in detail.
According to her, it is well known that anticoagulants are on the one hand very effective, however, on the other hand, when not being compliant with/to therapy recommendations, could lead to serious bleedings. This is one reason why patients with atrial fibrillation are still undertreated with oral anticoagulants (under-anticoagulation) – and if they are treated, there are still concerns in terms of potential bleeding complications. As a consequence, the therapeutic range of INR values is often set at a rather low level. This tendency is also reflected in the scientific publications. Another focus of her article is the over-anticoagulation in order to achieve/provide a better understanding of the various reasons and risks of higher INR values. This problem is also reflected in the daily experience of physicians, facing bleeding complications due to INR values above therapeutic target range.
Nevertheless, INR values that are below the therapeutic target range over a longer period of time, can lead to serious thromboembolic events.

According to the results of her study, Eva K Rombouts, Leiden (Thrombosis and Haemostasis 2009; 3:552-556), comes to the conclusion that patients taking acenocoumarol were long-term twice as often below their therapeutic target range than patients taking phenprocoumon. This was also applicable to patients having to stay in a higher therapeutic target range. Remarkably, 30% of the patients being below their therapeutic target range have either received vitamin K or the intake of oral anticoagulants has been stopped (unterbrochen) shortly before the measurement/study.

Finishing her editorial, E. Hylek points out that it is time by now to scientifically discuss and analyze the topic of INR values being below the therapeutic range over a longer period of time as there are still many questions open. In the meantime, it is a necessity that the oral anticoagulation therapy is going to improve further.

What can we do about it? We continue determining our INR values on a weekly basis and adjust our dosage accordingly. Let me finish with additional good news: according to a study from Fihn et al (2003) patients taking phenprocoumon are more stable and show fewer INR deviations.

Christian Schaefer, ISMAAP (10, 2009)