At the time of the introduction of direct oral anticoagulants (DOACs) in the beginning of this century, episodic and routine monitoring of these drug concentrations was deemed unnecessary. Unlike oral vitamin K anticoagulation, DOACs showed predictable pharmacokinetics and pharmacodynamics. However, once in clinical practice it became clear that under specific circumstances predictability of drug concentrations was less than optimal. During his educational presentation, Prof Johathan Douxfils (Univeristy of Namur) provided some answers to the questions why, when, and how we should measure DOAC concentrations.