A new global test for the evaluation of the activated factor II-antithrombin system

We developed a new simple test to evaluate the global function of the activ ated 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 (T-a) and without (T -o) heparin. The prolongation of clotting times (T-a - T-o) is directly rel ated to the function of the activated factor II-antithrombin system. The pr esence of quantitative or functional defects of the natural inhibitors (ant ithrombin and heparin co-factor II), or high levels of factor II and/or fib rinogen, can trigger a resistance to the inhibition of activated factor IL This new test was used to examine 134 thrombophilic patients as well as 157 normal subjects as controls. The results obtained confirm that the presenc e 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 accoun ted 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 f or evaluating the global function of the activated factor II-antithrombin s ystem in screening thrombophilic patients, alongside the tests already know n and used to diagnose these patients. <(c)> 2001 Lippincott Williams & Wil kins.