Summary
Relipidated recombinant tissue factor (r-TF) has been assessed in comparison with
conventional rabbit brain thromboplastin (Manchester Reagent) for its suitability
for measurement of prothrombin time (PT). The International Sensitivity Index (ISI)
of r-TF calibrated against the International Reference Preparation BCT/253 (human
plain) was found to be 0.96 and 1.12 with instrumental and manual techniques. Our
study of plasmas from patients with congenital deficiencies of clotting factors covering
a wide range of severity demonstrates that r-TF is able to detect even minor deficiencies
of factors involved in the extrinsic and common coagulation pathways. Patients with
liver diseases were correctly diagnosed with a prevalence of abnormal results comparable
for both reagents. Between-assay reproducibility expressed as coefficient of variation
was 2.3 % and 3.9 % at normal and abnormal PT levels.
In conclusion, our evaluation shows that relipidated r-TF possesses the necessary
requisites of sensitivity, diagnostic accuracy and reproducibility which make it a
suitable candidate for PT determination both for monitoring oral anticoagulant therapy
and diagnosing congenital and acquired clotting factor deficiencies. Moreover, being
a highly defined reagent it may constitute a step forward in the standardization of
PT testing.
