Protein C and S Immunoassay
Stephen Duff of Precision BioLogic asked me this question last week, driving me to my Colman, Kitchens, and even Esoterix' Coagulation Handbook. They had nothing, so I turned to manufacturers' package inserts. Most state the immunoassay results are reduced in Warfarin therapy, in particular the free protein S assay, but none says why, nor gives a reference.
You would think the immunoassay would remain near the normal range since we still produce protein C and protein S molecules, albeit non-carboxylated (called proteins in vitamin K antagonism, or PIVKA), but somehow the des-carboxy protein C and protein S molecules are not measured.
If anyone has an insight, please send a response here. For more on protein C and S, go to our educational module series, Laboratory Detection of Thrombosis Risk. Thanks. Geo.
