CPT® Code 85307

An Activated Protein C (APC) resistance assay is a specialized laboratory test designed to evaluate patients who have experienced unexplained venous thromboembolism (VTE). This assay is particularly focused on identifying a specific genetic mutation known as Factor V Leiden, which is a single point mutation in the Factor V gene. The presence of this mutation can significantly increase the risk of developing abnormal blood clots. The test involves comparing the patient's blood sample to a control sample that contains Factor V deficient plasma. By adding Activated Protein C to both samples, the assay assesses how the blood's clotting ability is affected. In a normal scenario, the addition of APC leads to a significant prolongation of the activated partial thromboplastin time (aPTT), indicating normal function. However, if the Factor V Leiden mutation is present, the prolongation will be less pronounced compared to the control, allowing for the determination of APC resistance. The results are quantified by calculating a ratio of the aPTT with APC to the aPTT without APC for both the patient and control samples, providing a clear indication of whether the mutation is present or absent.