USE OF INR FOR THE EXPRESSION OF PT IN PATIENTS UNDER ORAL ANTICOAGULANTS : COMPARISON OF RESULTS OBTAINED WITH FIVE THROMBOPLASTINS AND THREE DEVICES

The aim of our study is to know if INR (International Normalized Ratio) is really the best way to express PT (Prothrombin Time) in patients under oral anticoagulants (AVK). In this way, PT of 85 patients treated by AVK and 30 normal controls were determined with 5 different reagents and three devices : manual technic, KC10 (AHS Dade), Coag A Pet 200 (Gal Diagnostics, Organon). The reagents were : Thromborel S (Behring) extracted from human placenta, Thrombotest (Nyegaard) from ox brain, and 3 rabbit thromboplastins : Neo-plastine (Diagnostica Stago), Thromboplastine calcique (Bio-Merieux), Simplastin + (Gal Diagnostics). The results are expressed in seconds, percentage according to the dilution curve and INR with ISI given by the manufacturers.

Analysis of results shows :

- Influence of the technic : Whatever the technic is, mean results obtained with the same reagent, expressed in % are very close ; expressed in INR mean results are dispersed with all the reagents, ex :

- Influence of the reagent : Results performed with the same technic whatever the reagent is expressed in INR are very close, whereas in % the dispersion is large.

Analysis of variance and Student test show highly significant differences between all reagents for expression in %, whe reas expressed in INR (KC10) the difference is not statistical ly significant.

INR leads an improvement in the dispersion of results but it seems necessary to have at least two ISI for each reagent, one determined by manual technic or device like KC10, the other one determined on photo-optical device.