Dependent on Vitamin K, protein S is one of the proteins that are synthesized in the liver and endothelial cells and present in blood platelets. It is the part of the natural anticoagulant system and acts as the cofactor to activated protein C (APC) in the proteolytic inactivation of procoagulant factors Va and VIIIa. The patient of venous thrombosis has the Protein S deficiency. These deficiency tests are done in 3 forms by checking total protein S antigen, free protein S antigen, and protein S activity in plasma. When there are symptoms of recurrent miscarriage, complications of pregnancy (preeclampsia, abruptio placentae, intrauterine growth restriction, and stillbirth) and possibly arterial thrombosis then this test is suggested.