 Behavior A: Some physicians simply let the patient continue with the same dose. It is extremely unlikely that the very temporary dose adjustment has any effect on the PT result 4 weeks later and this is a cosmetic procedure. Behavior B: Others recommend the patients to take 12 - 1 additional dose in case of short PT and to skip a dose or take half dose in case of long PT, and thereafter to continue with the usual dose. The investigators need to quickly correct the temporary aberration in order to avoid thrombotic or bleeding complications the next few days. 