Comparative evaluation of five different methods for the measurement of plasma factor II levels in carriers of the 20210A prothrombin variant.

The common genetic G to A variation of the prothrombin gene is associated with elevated levels of prothrombin [factor II (FII)] and is recognized as a risk factor for thrombosis. To determine whether one type of assay for plasma FII measurement was more efficient than other assays in displaying high FII levels in 20210A carriers, we compared five methods of measuring FII levels [i.e. an enzyme-linked immunosorbent assay (ELISA), a standard clotting assay, and three chromogenic methods using three different activators: Ecarin, Oxyuranus, and Textarin] in 30 G20210A patients and 30 G20210G controls. Plasma concentrations of factor X and factor VII + factor X were also determined by a clotting procedure. Functional assays were found to be equally efficient in demonstrating significantly higher FII levels in 20210A carriers than in non-carriers (P < 0.0001). With ELISA, the difference observed was less significant (P < 0.005). The specificity of every assay increased with FII cut-off levels; when a cut-off of 115% was applied, sensitivities of functional assays were between 73 and 93%, while sensitivities of ELISA declined dramatically to 33%. FII/factor X and FII/factor VII + factor X ratios were significantly higher in 20210A carriers (P < 0.0001). In conclusion, functional assays are preferentially required for measurements of FII levels in carriers of the 20210A variant.

[Rapid determination of protein C activity]. / Dosage rapide de l'activité de la protéine C.

The diagnosis of Protein C (PC) congenital deficiency is of first importance because it leads, more frequently than Antithrombin III deficiency, to serious thromboembolic accidents in young patients, even when PC levels are slightly decreased (40 p. cent up to 60 p. cent). In order to measure PC activity, the authors developed a new method using the activator from Agkistrodon C. Contortrix snake venom and the synthetic chromogenic substrate CBS 65-25. Results obtained on plasma from normal individuals, congenital and acquired deficiencies, are comparable on the one hand, to those found with an ELISA method, and on the other hand with the clotting method, except for patients under anticoagulant therapy. This new rapid and sensitive method can be performed manually and is easily adapted on instruments used in clinical chemistry laboratories. This method is potentially available for routine use.