[Importance of standardization in the biological monitoring of anti-vitamin K therapy].

The aim of this work was to study certain causes of variation in the results of laboratory monitoring of treatment with vitamin K antagonists. Four centers participated in the study. In the initial phase, each center performed fifteen measurements of prothrombin time (PT) and activated partial thromboplastin time (APTT) on the same standard lyophilized plasma using its own usual reagents and its own methodology (protocol I). In the second phase of this study, each laboratory performed PT and APTT measurements on 30 frozen plasma specimens from patients receiving long term treatment with vitamin K antagonists using protocol I and protocol II (common reagents but own methodology). In the third phase, plasma from 19 patients receiving long term therapy with vitamin K antagonists were tested with common reagents and a standardized methodology (protocol III). the intralaboratory reproductability was very good; however, the use of common reagents and the standardization of methods greatly improved the intercenter reproductability. The use of common reagents allowed a stricter and a less contradictory interpretation of the tests.