Coagulation laboratory tests

Factor V Leiden assay

Last author update: 1 June 2012
Last staff update: 17 September 2020

Copyright: 2002-2024,, Inc.

PubMed Search: Factor V Leiden assay [title]

Jeremy C. Parsons, M.D.
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Cite this page: Parsons JC. Factor V Leiden assay. website. Accessed February 23rd, 2024.
Definition / general
  • Term is used interchangeably with activated protein C resistance (APCR) since Factor V Leiden causes most (but not all) cases of APCR
  • Test uses plasma (in citrate tube) for screening assay and whole blood for DNA based confirmation assay

  • Procedure:
    • Dilute patient plasma 1 : 5 with factor V deficient plasma (dilutes the effect of other factor deficiencies or elevations) and add polybrene (neutralizes unfractionated heparin or low molecular weight heparin)
    • If lupus anticoagulant is present, must perform DNA based test for Factor V Leiden (or perhaps 1 : 40 dilution of plasma or add phospholipids to neutralize lupus anticoagulant)
    • Calculate ratio of PTT with versus without exogenous activated protein C; normal is 2.0 or more, factor V Leiden usually < 2.0 (sensitivity and specificity approach 100%, because these patients activated factor V resists activated protein C degradation)

  • Many feel that positive results should be confirmed with a genetic assay

  • Other assays:
    • Prothrombin - based factor V assay with factor V deficient plasma (no interference from lupus anticoagulant)
    • Modified Russell viper venom time test (high phospholipids neutralizes lupus anticoagulant)
    • Factor Xa - based assay with factor V deficient plasma
    • DNA based tests such as PCR (using whole blood, not plasma)

  • Absence of MnlI cleavage at mutation site, guanine to adenine at #1691, or arginine to glutamine at amino acid #506 indicates factor V Leiden mutation
  • Additional references
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