In US: For Research Use Only. Not for Use in Diagnostic Procedures. Two-site ELISA method for the measurement of total Protein S (free or complexed with C4b-BP), in human citrated plasma. Assay designed with two conformational Murine monoclonal antibodies, calcium dependent, the first one for coating the microplate (immunocapture) and the second one, labeled with a Horse Radish Peroxidase (HRP) marker.