Protein S.

Area of Science:

• Biochemistry
• Hematology
• Molecular Biology

Background:

• Protein S (PS) is a vitamin K-dependent glycoprotein crucial for regulating blood coagulation.
• Free PS acts as a cofactor for activated protein C (APC) and also possesses APC-independent inhibitory functions.
• Deficiencies in PS, either acquired or hereditary, lead to uncontrolled thrombin generation and thrombophilia.

Purpose of the Study:

• To evaluate the diagnostic utility of various assays for Protein S deficiency.
• To compare the effectiveness of functional and immunological assays in detecting PS defects.
• To provide guidance on appropriate testing strategies for PS deficiency, considering potential interferences.

Main Methods:

• Review of existing literature on Protein S function and deficiency testing.
• Analysis of the advantages and limitations of functional PS assays versus immunological assays (free and total PS).
• Consideration of interference factors, such as lupus anticoagulant (LA), in assay selection.

Main Results:

• Hereditary PS deficiencies are caused by numerous mutations, making DNA sequencing impractical for routine diagnosis.
• Functional PS assays can detect deficiencies missed by free PS immunoassays.
• PS antigen assays are widely adopted in laboratories, but functional assays offer complementary diagnostic information.
• Functional assays are susceptible to interference, necessitating careful interpretation and specific recommendations in cases like LA presence.

Conclusions:

• Functional PS assays, alongside free PS immunoassays, are recommended for initial testing of PS deficiency, despite potential interferences.
• The choice of assay may depend on specific clinical contexts, such as the presence of lupus anticoagulant.
• Routine molecular characterization of PS mutations is not currently indicated for clinical management of thrombophilia.