AbstractAssays in the coagulation laboratory are affected by numerous variables. Variables which have impact on the test result can lead to incorrect results, and potentially to consequences for further diagnostic and therapeutic decisions made by the clinician. The interferences can be separated into three main groups: biological interferences, with an actual impairment of the patient's coagulation system (congenital or acquired); physical interferences, which usually occur in the pre-analytical phase; and chemical interferences, because of the presence of drugs (mainly anticoagulants) in the blood to be tested. This article discusses some of these interferences in seven instructive cases of (near) miss events as an approach to generate more attention to these issues.