[Clinical usefulness of global assays of the anticoagulant pathway of protein C]

Abstract

Abnormalities of the protein C anticoagulant pathway i.e. protein C and protein S deficiencies and factor V Leiden-related activated protein C resistance are among the most frequent risk factors for thrombosis in the Caucasian population. Until now, their screening is based upon the use of individual assays for each component. However, normal results are found in more than 70% of the tested patients. So, there was a rational behind the development of global assays to evaluate the functionality of the protein C pathway, as this would rationalize the use of costly specific assays. Such global assays are based on the ability of endogenous activated protein C generated by activation of protein C by a snake venom extract to prolong a clotting time. Up to now, two assays are commercially available, the ProC Global assay (Dade Behring) and the Protein C Pathway Test (Gradipore). Both were found to be highly sensitive for the factor V Leiden and for protein C deficiency, as confirmed by different studies in patients with a history of venous thrombosis. However, sensitivity of both global assays for protein S deficiency was found to be only moderate and highly variable depending of the cut-off level used. So, these global assays can be validly used for the screening of the factor V Leiden-related APC resistance and for protein C deficiency, but protein S have to be measured in all the cases. The overall sensitivity of these assays for abnormalities of the protein C pathway was dramatically different, since 40% of the patients without any known abnormality have a decreased response to the ProC Global assay versus less than 13% for the Protein C Pathway Test. These characteristics suggest that the clinical usefulness of these two global assays might be different.