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Coagulation

Coagulation laboratory tests

Factor V Leiden assay


Reviewer: Jeremy Parsons, M.D. (see Reviewers page)
Revised: 20 June 2012, last major update June 2012
Copyright: (c) 2002-2012, PathologyOutlines.com, Inc.

General
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● 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:
(1) 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)
(2) 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)
(3) 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 patientís activated factor V resists activated protein C degradation)

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

Other assays:
(a) Prothrombin-based factor V assay with factor V deficient plasma (no interference from lupus anticoagulant)
(b) Modified Russell viper venom time test (high phospholipids neutralizes lupus anticoagulant)
(c) Factor Xa-based assay with factor V deficient plasma
(d) 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

Diagrams
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Testing algorithm

Additional references
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Arch Pathol Lab Med 1998;122:430

End of Coagulation > Coagulation laboratory tests > Factor V Leiden assay


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