protein S activity in plasma (protein S assay)

Indications

• hypercoagulability without other explanation
• not routinely indicated in hypercoagulability workup

Reference interval

• total protein S:
  • 70-140% of normal reference activity
  • 0.67-1.25 U/mL
  • 21-42 ug/mL
• free protein S (active form)
  • 60-120% of normal reference activity
  • 0.23-0.49 U/mL

Increases

• pharmaceutical agents:
  • chemical interferences
    • heparin, warfarin
• clinical disorders

Decreases

• pharmaceutical agents
  • in vivo effects
    • oral contraceptives, L-asparaginase
• clinical disorders: hypercoagulability
  • congenital Protein S deficiency
    • low functional & antigenic levels
    • low functional & normal antigenic levels
  • acquired Protein S deficiency
    • liver disease
    • increases in C4-binding protein may result in increased binding of protein S & decreased levels of free (active) protein S
      • inflammatory syndromes
      • estrogens, pregnancy
    • acute thrombosis
    • vitamin K deficiency, warfarin therapy
    • protein losing enteropathy
  • only very low levels of plasma protein S (homozygous gene deletion) are associated with hypercoagulability

Methods

• functional* clotting assay based on anticoagulant activity
• rocket immunoelectrophoresis
• enzyme-linked immunosorbant assays (ELISA)
• microlatex particle mediated

* NOT useful if patient is anticoagulated

Specimen

• plasma (citrate)
• stable at room temperature for 8 hours
• stable at -20 degrees C for 1 month

More general terms

• clinical hematology test

Additional terms

• free protein S in plasma
• protein S antigen in plasma
• protein S deficiency
• protein S; vitamin K-dependent protein S (PROS1, PROS)

Patient information

protein S assay patient information