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Test Mnemonic:


Specimen Requirements:

Blue-topped (3.2% sodium-citrate) tube. Routine venipuncture; discard 1st mL of blood by collecting a discard tube prior to collecting the blue-topped (3.2% sodium-citrate) tube.  For collections with butterfly blood collection sets, a discard tube should also be collected prior to collection of the blue top to ensure sufficient sample volume. Drawing a discard tube will displace the air from the blood collection set tubing to ensure proper blood draw volume.


 Blue-topped (3.2% sodium-citrate) tube


OTE: If delivery time is to be greater than 24 hours from time of draw, double centrifuge the specimen. Centrifuge sample for 20 minutes at 2000g. Transfer plasma to 12x75 plastic tube. Cap tube and re-spin for 20 minutes at 2000g. CAREFULLY remove from centrifuge without disturbing any platelets and/or cell pellets that might be on the bottom or sides of the tube. Carefully transfer plasma into freezer tubes (plastic screw-top cryo-tubes) for testing or freezing.

Specimen Preparation:

Acceptable up to 24 hours after draw, at ROOM TEMPERATURE.


Whole Blood 24 hours at room temperature.  Plasma may be stored frozen at -20°C for 2 weeks, or -70C for 3 years.

Causes for Rejection:

QNS, clotted, severely hemolyzed, greater than 24 hours old, wrong tube (3.8% sodium citrate), high hematocrit (> 55%), sample identification error, processed and/or stored improperly.

Reference Range:

APCR Ratio > 2.0 (Normal)

Turnaround Time:

 Test performed once per week (batch); maximum 7 day turnaround time. Call Laboratory for schedule


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


Samples are accepted 24 hours per day at Sample Management, 7.412 CSW Bldg.



Clinical Indication:

A screening assay for the detection of activated protein C resistance (APCR) in patients with 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).

Patient Preparation :

Patient should be at rest for 10 minutes prior to collection.

CPT 4 Code:



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.

Critical Values: No stated critical value.  Borderline and positive results should be repeated and/or confirmed with Factor V Leiden testing.

When ordering tests for which Medicare or Medicaid reimbursement will be sought, physicians should only order tests that are medically necessary for the diagnosis or treatment of the patient. Components of the organ or disease panels may be ordered individually. The diagnostic information must substantiate all tests ordered and must be in the form of an ICD-10 code or its verbal equivalent.
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