Protein S (PS)*

Congenital or acquired PS deficiencies are associated with an increased risk of venous thromboembolism.
In the early stages of inflammatory diseases, free PS concentration is decreased because of an elevation of C4b-BP. PS may be decreased in various contexts such as dicoumarol or L-asparaginase therapy, in hepatic disorders, nephrotic syndrome, during pregnancy, related to oral contraceptives intake or œstrogen therapy, viral infections, DIC. Free PS may also be decreased in new-borns. PS is slightly lower in females than in males.
Inherited PS deficiencies are classified into three types:
   • Type I: decreased total and free PS levels (quantitative defects).
   • Type II: decreased PS activity but normal antigenic levels (rare qualitative defects).
   • Type III: normal levels of total PS but decreased free PS (free form distribution defect).


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