title: Improved distinction of factor V wild-type and factor V Leiden using a novel prothrombin-based activated protein C resistance assay.
abstract: A new prothrombin-based activated protein C resistance (APC-R) test is described. In this method, the patient sample is prediluted in a plasma depleted of factor V (FV). A reagent containing APC and a specific activator of FV is added. After an incubation period, clotting is initiated by the addition of the FV-dependent prothrombin activator Noscarin. We analyzed 703 samples from patients undergoing thrombophilia screening. By using a predefined cutoff ratio of 2.5, 100% sensitivity and specificity for the detection of a factor V Leiden (FVL) mutation was found. With a cutoff ratio of 1.2, a complete but narrow distinction of FVL heterozygous (n = 192) and FVL homozygous samples (n = 27) was determined. No interference by the international normalized ratio, activated partial thromboplastin time (aPTT), protein S activity, fibrinogen and factor VIII (FVIII) levels, or lupus anticoagulant ratio was detected. The new prothrombin-based APC-R assay provides improved distinction of FV wild-type and FVL carriers compared with the aPTT-based method. By the use of an FV-dependent prothrombin activator, the assay is not influenced by FVIII concentration or lupus anticoagulants.
authors.affiliation: Research and Development Haemostasis, Pentapharm, Basel, Switzerland.
authors.forename: Marianne
authors.initials: M
authors.lastname: Wilmer
authors.forename: Christoph
authors.initials: C
authors.lastname: Stocker
authors.forename: Bea
authors.initials: B
authors.lastname: Bühler
authors.forename: Brigitte
authors.initials: B
authors.lastname: Conell
authors.forename: Andreas
authors.initials: A
authors.lastname: Calatzis
mesh_terms: D001780:Blood Coagulation Tests / Q000379:methods*; D005165:Factor V / Q000032:analysis* / Q000235:genetics; D005166:Factor V Deficiency / Q000097:blood*; D006801:Humans; D009154:Mutation; D011486:Protein C / Q000378:metabolism*; D011516:Prothrombin / Q000378:metabolism*; D012680:Sensitivity and Specificity
chemical_list: D011486:Protein C; D005165:Factor V; D011516:Prothrombin