ACTIVATED PROTEIN C RESISTANCE: (089-0240)

 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).

APCR

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

 Samples are accepted 24 hours per day at Sample Management, 5.136 McCullough Bldg.

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

Patient Preparation: Patient should be at rest for 10-20 minutes prior to collection.

Collect:   Routine venipuncture; discard 1st mL of blood or collect other tubes (EDTA, red-topped) prior to collecting sample in (2)blue-topped (3.2% sodium-citrate) tubes.

Specimen Preparation:  Samples should be received in laboratory within ½ hour of draw for best results.  Acceptable up to 4 hours after draw, at ROOM TEMPERATURE.

Specimen: Blood

Volume: 2.7ml

Minimum Volume: Call Lab

Storage/Transport: NOTE: If delivery time is to be greater than 4 hours from time of draw, centrifuge the sample, separate the plasma from the cells and snap freeze (-20⁰C) the plasma.

Stability:  Snap frozen plasma is viable for 6 months.

Causes for Rejection: QNS, clotted, severely hemolyzed, greater than 4 hours old, wrong tube (3.8% sodium citrate), high hematocrit (> 55%), identification error, processed and/or stored improperly.

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 by The Antiphospholipid Laboratory (Dr. Sylvia Pierangeli)

APCR Ratio > 2.2 (Normal)

 85307

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-9 code or its verbal equivalent.

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