[Study of present possibilities of interlaboratory standardisation of the prothrombin time (author's transl)].

The graphs or tables proposed by the manufacturer of reagents, the Thivolle straight lines suggested by Raby or, since 1977, Loeliger's procedure, are three possibilities offered to biologists to transform the prothrombin time into prothrombin concentrations expressed as a percentage. We have studied the possibility of interlaboratory standardisation in the case of patients treated with coumarin derivatives: firstly with the same thromboplastin under various conditions of use; secondly with five different thromboplastins under identical conditions (choosing arbitrarily one of the reagents as reference). Loeliger's procedure is the one which permits the best standardisation, but its practical application seems difficult. It seems to us that before carrying out this standardisation between laboratories, one should indicate, with the result found for the patient, the area of therapeutic activity of the thromboplastin used, as suggested by Ducker and Marbet in 1977 (these authors determined this area of therapeutic activity for 13 different reagents used in Switzerland).