High normal or increased total protein S antigen and reduced free protein S antigen suggests acquired protein S deficiency, as may be seen in pregnancy or inflammation. However, the total protein S antigen level may be helpful in distinguishing acquired versus congenital protein S deficiency. Protein S and C4bBP are coordinately regulated, and an increased total protein S antigen and low free protein S antigen most commonly reflect acute or chronic inflammation or illness with an associated increase in plasma C4bBP.įor patients in whom hereditary protein S deficiency is strongly suspected and the free plasma protein S antigen level is normal, consideration should be given to testing of free protein S activity, S_FX / Protein S Activity, Plasma, for detecting type II protein S deficiency (which is rare).Īn increased total protein S antigen is of uncertain clinical significance because free protein S antigen levels are usually normal, in such situations. Types of Heterozygous Protein S Deficiency Protein S values vary widely in the normal population and are age- and sex-dependent. When the free protein S antigen level is below the age- and sex-adjusted normal range, reflexive testing will be performed for total plasma protein S antigen. Measurement of plasma free protein S antigen is performed as the initial testing for protein S deficiency. As an acute-phase reactant, plasma C4bBP levels increase with acute illness and may cause acquired free protein S deficiency. Acquired protein S deficiency can present through vitamin K deficiency, oral anticoagulant therapy, liver disease, DIC/ICF, thrombotic thrombocytopenia purpura, pregnancy or estrogen therapy, nephritic syndrome, and sickle cell anemia. Homozygous protein S deficiency is rare, but can present as neonatal purpura fulminans, reflecting severe disseminated intravascular coagulation/intravascular coagulation and fibrinolysis (DIC/ICF) caused by the absence of plasma protein S.Īcquired deficiency of protein S has causes that are generally of unknown hemostatic significance (ie, uncertain thrombosis risk), and is much more common than hereditary protein S deficiency. Type III protein S deficiency appears to be partly due to mutations within the protein S binding region for C4bBP-beta. Types I and III protein S deficiency are much more common than type II (dysfunctional) protein S deficiency. Three types of protein S deficiency have been described according to the levels of total protein S antigen, free protein S antigen, and protein S activity in plasma. In addition they may also experience recurrent miscarriage, complications of pregnancy (preeclampsia, abruptio placentae, intrauterine growth restriction, and stillbirth) and possibly arterial thrombosis. Patients with protein S deficiency have an approximately 10-fold increased risk of venous thrombosis. Different C4bBP isoforms are present in plasma, but only C4bBP-beta binds protein S.Ĭongenital protein S deficiency is an autosomal dominant disorder that is present in 2% to 6% of patients with venous thrombosis. C4bBP is composed of 6 or 7 alpha-chains and 1 or no beta-chain (C4bBP-beta). Only free protein S has anticoagulant function. Of the total plasma protein S, approximately 60% circulates bound to C4bBP, while the remaining 40% circulates as free protein S. In human plasma, protein S forms a complex with the compliment regulatory protein, C4b-binding protein (C4bBP). In addition, protein S has direct APC-independent anticoagulant activity by inhibiting formation of the prothrombin and tenase complexes, possibly due to its high affinity for anionic phospholipid membranes. Protein S works as part of the natural anticoagulant system by acting as a cofactor to activated protein C (APC) in the proteolytic inactivation of procoagulant factors Va and VIIIa. Protein S is a vitamin K-dependent glycoprotein present in platelets and synthesized within the liver and endothelial cells. Each coagulation assay requested should have its own vial. Double-centrifuged specimen is critical for accurate results as platelet contamination may cause spurious results.Ģ. Send specimens in the same shipping container.ġ. Freeze plasma immediately (no longer than 4 hours after collection) at -20 degrees C or, ideally, < or =-40 degrees C.Ĥ. Configure, remove plasma, and spin plasma again.ģ. For complete instructions, see Coagulation Guidelines for Specimen Handling and Processing.Ģ. Specimen Volume: 1 mL in 2 plastic vials each containing 0.5 mLġ. Coumadin will lower protein S.Ĭollection Container/Tube: Light-blue top (3.2% sodium citrate) If the patient is being treated with Coumadin, this should be noted. Patient Preparation: Patient must not be receiving heparin or Coumadin. For more information see PSTF / Protein S Antigen, Plasma.
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