MULTICENTRIC EVALUATION OF A NEW PT REAGENT BASED ON RECOMBINANT HUMAN TISSUE FACTOR AND SYNTHETIC PHOSPHOLIPIDS

A new PT reagent based on recombinant human tissue factor and syntheti c phospholipids (phosphatidyl choline and phosphatidyl serine) with de fined fatty acid side chains was calibrated against BCT/253 and CRM 14 9R. A small but consistent bias in the International Sensitivity Index (ISI) value was obtained using either the human or rabbit brain refer ence material. ISI values were around 1.0 or slightly lower depending on the respective instrument. Mixing studies with factor deficient pla smas showed a high factor sensitivity especially for factor VII as com pared to commercial rabbit brain or human placenta thromboplastin. In an international field trial the reagent was tested using fully or sem i automated Electra(TM) Coagulometers in 4 different laboratories. Res ults with normal samples were in excellent agreement among the differe nt laboratories. Mean values were 10.9, 10.9, 11.0, 11.2 s with a rang e of 9.5 to 12.5 s. Results of males and females were not different. I n patients with liver disease very similar PT activities were found as compared to sensitive rabbit brain or human placental thromboplastins . In normals and patients with oral anticoagulation INR values correla ted very well against BCT (r = 0.98, regression line y = -0.07 + 0.9 x ). The distribution of samples was linear over the whole range. In the comparison against sensitive rabbit brain thromboplastin or human pla cental thromboplastin similar correlations were found. In a few cases higher INR values were observed for the recombinant reagent especially in patients with intensive treatment. Factor assays in those patients showed at least the strong reduction of one vitamin K-dependent coagu lation factor. Over all the linearity was better against the rabbit br ain reagent than against the human placental reagent which is slightly less factor VII sensitive as shown in mixing studies with normal and factor VII deficient plasma. Precision studies in the 4 laboratories s howed excellent reproducibility of lyophilised controls or local patie nt plasma pools for all reagents with a better performance of the reco mbinant reagent. C. V. values from day to day ranged from 1.3% to 5% f or normal and abnormal controls. These results show that the recombina nt PT reagent, especially in conjunction with a precise automated inst rument, may improve the results of PT testing and thus may lead to bet ter patient care.