Free Protein S details

Free Protein S measures the portion of Protein S — a natural anticoagulant protein — that circulates unbound and biologically active, as opposed to the portion bound to a carrier protein. Since the free fraction is the part that actually does the anticlotting work, this is often considered the more clinically useful measurement than total Protein S. Low free Protein S, whether from an inherited deficiency or acquired causes (like pregnancy, liver disease, or certain medications), raises the risk of abnormal blood clot formation, and it's typically tested as part of a broader clotting disorder workup after an unexplained blood clot.