A new chromogenic assay (HemosIL ThromboPath) is sensitive to major prothrombotic risk factors affecting the protein C pathway. Results of a multicenter study.

The HemosIL ThromboPath assay (Instrumentation Laboratory) is a new chromogenic assay designed to globally evaluate the functionality of the protein C (PC) pathway. It is based on the ability of endogenous APC generated after activation of PC by a snake venom extract (Protac) to reduce the thrombin generation induced by a reagent containing tissue factor. The aim of this multicenter study involving three laboratories was to evaluate the test sensitivity to PC pathway abnormalities by retrospectively testing frozen plasma samples obtained in the different laboratories. Test results were significantly lower (p < 0.0001) in subjects who presented with any confirmed PC pathway abnormality than in those without. The cut-off value, defined in each participating center as the mean value minus one standard deviation of test results obtained in 30 normal samples, was found to provide a sensitivity-to-specificity ratio similar to that obtained using ROC-analysis. The assay performed well in carriers of the factor V Leiden mutation (n = 81), patients with PC deficiency (n = 40), combined defects (n = 55) or lupus anticoagulant (n = 44), with test results below the locally defined cut-off values in 97.5%, 95.0%, 100% and 100% of the tested subjects, respectively. The assay sensitivity for PS deficiency (n = 62) was 87.1%. Only 13.6% of the 272 subjects without any PC pathway abnormality had a decreased test result. So, using the locally defined cut-off values, the overall test sensitivity to all tested PC pathway abnormalities was 95.0% (95%CI = 91.8-97.3), its specificity 86.4% (95%CI = 81.8-90.2), its negative predictive value 94.4% (95%CI = 90.8-96.9) and its positive predictive value 87.9% (95%CI = 83.7-91.3).