CALIBRATED PLASMA PROCEDURE AND INR FOR PT STANDARDIZATION. DATA FROM THE FRENCH ETAL0N0RME QUALITY CONTROL SURVEYS

One of the aim of the survey conducted in last december 1986 was to assess the efficacy of 2 procedures of standardization :

1) the INR system, derived from thromboplastin calibration and adopted in 1983 by the WHO.

2) the Reference Calibrated Plasmas (RCP) procedure, evaluated on large scale, through French interlaboratory trials (1977-85), exhibiting net improvement of the dispersion of overall data.

Labs were asked to perform with their local thromboplastin and method, the PT of a human lyophilized plasma 86 H/I, originated from long term antivitarnines-K (AVK) treated patients. Results were expressed *in time ; *in % activity, according to the traditional procedure based on saline dilutions of normal plasma ; *in INR using the ISI of the local reagent calibrated by the manufacturer. Calibrated plasmas procedure allow the determination of corrected activity ; *in % activity and INR, according to the linear calibration curve obtained from the PT of 2 reference calibrated plasmas with determinated activities in INR and % activity. These RCP were provided with and tested under the same conditions as plasma 86 H/I6 (2 systems of RCP : AVK and artificially depleted).

Statistical analysis shows that the "RCP" procedure leads to the best improvement of the interlaboratory variation for the overall data, and the best uniformization of mean results, whatever the way of expression (%, INR), the thromboplastin brand, and the method of PT testing. Results play also in favour of a system of AVK reference plasmas, giving a better grouping than the artificial calibrated plasmas. The INR system nevertheless provides a common scale of data reporting, but might hold profit from an efficient procedure of standardization, such as the calibrated AVK plasmas procedure.

Coefficient of variation (CV) expressed in %. Overall data PT of 86 H/I. French Etalonorme Survey.