With the introduction of new anticoagulant agents, there is a need for information on which coagulation tests are most suitable. These agents react differently to assays used to monitor older anticoagulant agents because they have alternative modes of action. Therefore, other tests, or modifications of existing tests which are more appropriate for newer agents, are needed. The prothrombin time test (with conversion to the international normalized ratio) is usually used to monitor warfarin. However, conversion to the international normalized ratio is not appropriate for measuring the effects of fondaparinux, dabigatran, rivaroxaban or apixaban. Instead, chromogenic assays, one-step prothrombinase-induced clotting time test and the HepTest with reduced incubation time, are among the different or modified tests that appear to give the most reproducible and accurate results. The tests show variations in response to anticoagulants - some of which have clinical relevance. Thus, it is important to be aware of the observed variations in order to prevent the misinterpretation of test results.