title: Reliability of a modified tissue factor-dependent factor V assay for activated protein C resistant factor Va using a calcium-containing thromboplastin.
abstract: The original tissue factor-dependent factor V assay for activated protein C resistant factor Va (Blood 1995; 85: 1704-1711) has been modified to use a calcium containing thromboplastin and to express results as an observed to expected ratio (Obs/Exp.). The latter permits establishing a normal range independent of variations due to differences in reagents. Comparing Obs/Exp ratios with DNA analysis in 72 persons revealed that an Obs/Exp ratio of 0.6 distinguished without overlap normals from heterozygotes for FV R506Q. Three homozygotes had a ratio of < 0.1. Application of this Obs/Exp cut-off ratio of 0.6 to a total of 226 plasma samples tested to date discriminated without overlap between normals and heterozygotes. We conclude that this assay-readily adaptable to any dedicated coagulation laboratory and capable of yielding reliable results in all clinical circumstances in which testing is indicated-can distinguish between normals and heterozygotes for the FV R506Q mutation without the need for confirmatory DNA analysis.
authors.affiliation: Department of Pathology, University of California, San Diego, USA. dzle@ucsd.edu
authors.forename: D T
authors.initials: DT
authors.lastname: Le
authors.forename: K J
authors.initials: KJ
authors.lastname: Donnelly
authors.forename: N
authors.initials: N
authors.lastname: Wu
authors.forename: B K
authors.initials: BK
authors.lastname: Sevilla
authors.forename: S I
authors.initials: SI
authors.lastname: Rapaport
mesh_terms: D001760:Bleeding Time; D001774:Blood Chemical Analysis; D002118:Calcium; D004247:DNA / Q000032:analysis; D005165:Factor V / Q000032:analysis* / Q000235:genetics; D015943:Factor Va / Q000032:analysis* / Q000235:genetics; D006493:Heparin / Q000494:pharmacology; D006579:Heterozygote; D006801:Humans; D016682:Lupus Coagulation Inhibitor / Q000032:analysis; D009154:Mutation; D010976:Platelet Count / Q000187:drug effects; D011486:Protein C / Q000378:metabolism*; D015203:Reproducibility of Results; D013925:Thromboplastin / Q000378:metabolism*
chemical_list: D016682:Lupus Coagulation Inhibitor; D011486:Protein C; D015943:Factor Va; D005165:Factor V; D006493:Heparin; D004247:DNA; D013925:Thromboplastin; D002118:Calcium