A novel combined ELISA assay demonstrates that specific conformational changes in protein C occur more rapidly than changes in prothrombin time at the initiation of oral anticoagulation.
May detect faster protein C changes than prothrombin time at anticoagulation onset; leaves open whether this refines clinical monitoring.
We have developed a variation of the solid-phase enzyme-linked immunosorbent assay (ELISA) to enable measurement of the activity and antigen levels of protein C (PC) in human plasma. With this assay it is possible to do both tests with the same sample and same microtiter plate coated with anti-PC monoclonal antibody (MCA)JTC-4, which inhibited neither activation of PC nor activity of activated PC (APC). Even in patients undergoing heparin treatment for severe disseminated intravascular coagulation, there were no detectable differences between amidolytic activity and antigen levels of PC in patients' plasma. In addition, there was a strong correlation between the immunologic levels of PC in patients' plasma determined both by polyclonal ELISA using peroxidase-labeled immunopurified antiprotein C-IgG and those found with MCA ELISA using peroxidase-labeled MCAJTC-5, which does not bind to APC. In contrast, when oral anticoagulation therapy was started, immunologic levels of plasma PC estimated by peroxidase-labeled MCAJTC-1, a MCA that recognizes a gamma-carboxyglutamic acid domain-related conformational change of PC induced by metal ions, decreased more rapidly than did either the PC level determined by polyclonal ELISA or the percent prothrombin time. This suggested that comparison of MCAJTC-1-recognized PC levels and prothrombin time may be necessary at the beginning of oral anticoagulation therapy to treat patients safely.
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Mimuro et al. (1987) studied this question.
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