Activated Protein C (APC) Resistance Test
Sample Type: Plasma

Purpose:
The APC Resistance test is primarily used to detect resistance to activated protein C, most commonly due to a genetic mutation known as Factor V Leiden. This mutation is a major inherited risk factor for venous thromboembolism (VTE), including deep vein thrombosis (DVT) and pulmonary embolism (PE).

Mechanism:
Activated protein C (APC) is a natural anticoagulant that inactivates clotting factors Va and VIIIa to help prevent excessive clotting. Resistance to APC means these factors are not adequately inactivated, increasing the risk of abnormal blood clot formation.

Indications for Testing:

Unexplained thrombosis, especially in young patients

Recurrent thrombotic events

Family history of thrombophilia

Evaluation of thrombophilia before hormonal therapy (e.g., oral contraceptives)

Work-up for pregnancy complications related to clotting

Sample Collection:

Collected in a citrate anticoagulant tube

Processed to obtain platelet-poor plasma

Must be tested within a specific time frame or frozen promptly for accuracy

Interpretation:

Normal APC sensitivity ratio suggests normal clotting regulation.

Decreased APC sensitivity ratio indicates resistance and warrants further testing (e.g., genetic test for Factor V Leiden).

Follow-up Testing:
If APC resistance is detected, DNA testing for the Factor V Leiden mutation is often recommended to confirm the diagnosis.