Haemostasis pp 373-381 | Cite as

Protein S

  • Mirta Hepner
  • Vasiliki Karlaftis
Part of the Methods in Molecular Biology book series (MIMB, volume 992)


Protein S (PS) is a vitamin K-dependent plasma glycoprotein. Around 60–70% of PS in plasma is noncovalently bound to C4-binding protein (C4BP). Free PS functions as a cofactor that enhances the activity of activated protein C (APC) in the proteolytic degradation of activated factors V and VIII. PS also has a more recently described APC-independent ability to directly inhibit prothrombinase and tenase by direct binding of activated factors V, VIII, and X.

Given that PS is one of the major naturally occurring inhibitors of coagulation, acquired or hereditary deficiencies of this protein result in excessive thrombin generation. As a vast array of mutations are responsible for hereditary PS deficiencies, screening for their presence by DNA testing would require sequencing each entire gene involving numerous exons. Moreover, the knowledge of the gene mutation does not offer any benefit in the treatment of thrombophilic families, so the routine molecular characterization is not indicative. These defects are detected by functional or immunological assays for free and total PS forms. Given that functional PS assays may detect some forms of PS deficiency that free PS immunoassays may miss, it is recommended to include them for initial testing along with immunoassays for free PS, although they should be used with caution. Functional PS assays are subject to multiple interference. For example in the presence of lupus anticoagulant (LA), only free PS immunoassays are recommended for initial testing. PS antigen assays are more popular with most laboratories.

Key words

Protein S Functional assay Immunological assays Blood coagulation inhibitor Acquired deficiency Hereditary deficiency 


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Copyright information

© Humana Press 2013

Authors and Affiliations

  • Mirta Hepner
    • 1
  • Vasiliki Karlaftis
    • 2
  1. 1.Laboratorio de Hemostasia y TrombosisHospital de Pediatría “Prof. Dr. Juan P. Garrahan”Buenos AiresArgentina
  2. 2.Haematology Research LaboratoryMurdoch Children’s Research InstituteMelbourneAustralia

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