Reliability of a modified tissue factor-dependent factor V assay for activated protein C resistant factor Va using a calcium-containing thromboplastin

• Published in: Thrombosis and haemostasis Vol. 77; no. 3; p. 481
• Main Authors: Le, D T, Donnelly, K J, Wu, N, Sevilla, B K, Rapaport, S I
• Format: Journal Article
• Language: English
• Published: Germany 01-03-1997
• Subjects: Bleeding Time; Blood Chemical Analysis; Calcium; DNA - analysis; Factor V - analysis; Factor V - genetics; Factor Va - analysis; Factor Va - genetics; Heparin - pharmacology; Heterozygote; Humans; Lupus Coagulation Inhibitor - analysis; Mutation; Platelet Count - drug effects; Protein C - metabolism; Reproducibility of Results; Thromboplastin - metabolism
• ISSN: 0340-6245
• DOI: 10.1055/s-0038-1655993

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.