Activated protein C resistance test

The Activated Protein C Resistance Test is a laboratory assay used to evaluate the resistance of blood plasma to activated protein C (APC). This test is primarily used to diagnose Factor V Leiden mutation, which is the most common hereditary cause of thrombophilia.

Background

Activated protein C is a natural anticoagulant that inactivates Factor Va and Factor VIIIa, thereby reducing thrombin generation and preventing excessive blood clotting. Resistance to activated protein C is often due to a genetic mutation in the Factor V gene, known as Factor V Leiden, which makes Factor Va resistant to inactivation by APC.

Test Procedure

The activated protein C resistance test is performed by measuring the clotting time of plasma in the presence and absence of activated protein C. The test is typically conducted using a partial thromboplastin time (PTT) assay. The ratio of the clotting time with APC to the clotting time without APC is calculated. A lower ratio indicates resistance to activated protein C.

Clinical Significance

Resistance to activated protein C is associated with an increased risk of venous thromboembolism (VTE), including deep vein thrombosis (DVT) and pulmonary embolism (PE). Identifying individuals with APC resistance, particularly those with the Factor V Leiden mutation, is important for assessing thrombotic risk and guiding management strategies.

Interpretation

A normal result indicates that the plasma is sensitive to activated protein C, while an abnormal result suggests resistance. Further genetic testing may be performed to confirm the presence of the Factor V Leiden mutation.

Related Pages

• Factor V Leiden
• Thrombophilia
• Venous thromboembolism
• Partial thromboplastin time

Gallery

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  Thrombin generation curves with and without activated protein C.