RESUMO
We developed a new simple test to evaluate the global function of the activated factor II-antithrombin system. The new test measures the clotting time of plasma samples after the addition of a reagent containing a snake venom (Echis carinatus) that can activate prothrombin, with (Ta) and without (To) heparin. The prolongation of clotting times (Ta - To) is directly related to the function of the activated factor II-antithrombin system. The presence of quantitative or functional defects of the natural inhibitors (antithrombin and heparin co-factor II), or high levels of factor II and/or fibrinogen, can trigger a resistance to the inhibition of activated factor II. This new test was used to examine 134 thrombophilic patients as well as 157 normal subjects as controls. The results obtained confirm that the presence of abnormalities relating to the activated factor II-antithrombin system causes a resistance to activated factor II inhibition even if a significant number of patients was found to have a resistance that could not be accounted for. Since the new test can be easily performed automatically and has a good inter- and intra-assay variation coefficient (CV < 4%) it is useful for evaluating the global function of the activated factor II-antithrombin system in screening thrombophilic patients, alongside the tests already known and used to diagnose these patients.
Assuntos
Antitrombinas/fisiologia , Coagulação Sanguínea/efeitos dos fármacos , Protrombina/fisiologia , Antitrombinas/farmacologia , Testes de Coagulação Sanguínea/métodos , Testes de Coagulação Sanguínea/normas , Estudos de Casos e Controles , Relação Dose-Resposta a Droga , Fator VIII/farmacologia , Feminino , Heparina/farmacologia , Humanos , Masculino , Programas de Rastreamento , Métodos , Protrombina/antagonistas & inibidores , Protrombina/efeitos dos fármacos , Protrombina/metabolismo , Protrombina/farmacologia , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Venenos de Serpentes/farmacologia , Trombofilia/sangueRESUMO
A functional clotting assay was recently reported to detect the factor V-Leiden mutation (R506Q) in patients receiving oral anticoagulants and in patients with Lupus Anticoagulant inhibitor. The original assay (Dahlback) to detect resistance to activated protein C (aPC-resistance) frequently gave unreliable findings in these patients. The change in the method is the use of bovine thromboplastin in a PT-derived assay, with a 1:10 sample dilution. In these conditions a reference normal plasma gives a prolongation of more than 35 seconds, while samples with a heterozygous or homozygous mutation give a prolongation respectively of 10-18 seconds or less 2 seconds. The test is easily automated and quickly performed on ACL/3000, and the reproducibility is good.