Activated protein C resistance test
medical diagnostic test
The activated protein C resistance (APCR) test is a coagulation test used in the evaluation and diagnosis of activated protein C (APC) resistance, a form of hypercoagulability. Hereditary APC resistance is usually caused by the factor V Leiden mutation, whereas acquired APC resistance has been linked to antiphospholipid antibodies, pregnancy, and estrogen therapy. APC resistance can be measured using either an activated partial thromboplastin time (aPTT)-based test or an endogenous thrombin potential (ETP)-based test.
Methodology
The aPTT-based APC resistance test involves a modified aPTT test performed in the presence and absence of activated protein C (APC). The ratio of these aPTT values is calculated and is called the APC sensitivity ratio (APCsr) or simply APC ratio (APCr). This ratio is inversely related to the degree of APC resistance. The ETP-based APC resistance test involves the addition of APC to a thrombin generation assay (TGA). This results in an inhibition of thrombin generation as measured by reduction of the endogenous thrombin potential (ETP; area under the thrombin generation curve). The result is expressed as a normalized APC sensitivity ratio (nAPCsr), which corresponds to the ratio of the ETP measured in the presence and absence of APC divided by the same ratio in reference plasma. nAPCsr values range from 0 to 10.
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