ACTIVATED PROTEIN C RESISTANCE

Applies To: A screening assay for the detection of activated protein C resistance (APCR) in patients with a history of recurrent venous thrombosis. Most patients with a positive APCR screening assay have a specific mutation in the coagulant factor V gene (Factor V Leiden mutation).

Test Includes: APCV Ratio; Interpretation of result.

Request Form: Hematology A

Collection: Patient should be at rest for 10-20 minutes prior to collection. Standard venipuncture collection for Coagulation specimens. Discard 1st ml of blood or collect other tubes (EDTA, Serum-separator, etc.) prior to collecting sample in 3.2% citrate (light blue-top) tube.

Storage Instructions: Viable for 4 hours at room temperature. If time from draw to delivery is to be greater than 4 hours, centrifuge the sample, separate the plasma from cells, and snap freeze (-70°C) the plasma. Snap frozen plasma is viable for 6 months.

Special Instructions: Prior to ordering this test, verify that the APTT is in the normal range.

Causes for Rejection: QNS, clotted, severely hemolyzed, greater than 4 hours old, identification error, improper processing or storage.

Availability: Accepted 24 hours/day at Sample Management, Room 5.136 McCullough.

Turnaround Time: Test performed once per week (batch); maximum 7 day turn around time. Call Laboratory for schedule.

Specimen: Blood

Volume: 4.5 mL

Min Volume: Call Lab

Container: 3.2 % Sodium citrate tube (light blue-top)

Reference Range: APCR Ratio > 2.2 (Normal)

Critical Values: No stated critical value. Borderline and positive results should be repeated and/or confirmed by Molecular Assay (Factor V Leiden, ARUP send out test).

Test Method: Electromagnetic Viscosity Detection; APTT-based; Ratio calculation and interpretation.

Interfering Substances: Activated Factor V and VIII due to improper collection; High inhibitor activity (e.g. phospholipid antibodies), heparin levels > 1 IU/ml.

Interpretation of Results: The responsiveness of plasma to activated protein C (APC) is measured as the ratio of two activated partial thromboplastin times, one in the presence of APC and one in its absence. Patients with APC resistance have a lesser prolongation of APC-PTT values compared to normal. Although most patients with a positive APCR screening assay have the Factor V Leiden mutation, other low-frequency factor V mutations are detected only by the screening assay. Thus, it is recommended that patients with recurrent venous thrombosis first be screened with the APCR assay. All positive APCR assays should then be confirmed with the Factor V Leiden Mutation Assay.

Revised 10/10/07 by W. Russo MT(ASCP)

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