Activated Protein C – Resistance

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Justification

Used to evaluate patients with recurrent venous thrombosis. This is a second generation function assay. While most instances of APC resistance (APCR) are caused by the presence of Factor V Leiden (FVL), APCR may be abnormal with less common Factor V mutations, heparin, oral anticoagulants, lupus anticoagulants or other acquired causes. In cases where APCR is abnormal but FVL testing is normal, sequencing of the Factor V gene may be warranted to detect rare variants.

STAT: < 48 hours (M-F)

Ratio, Clot-based

Draw Tube: Blue Top

Sample Type: Citrated Plasma

Specimen Requirements

	Sample Type	Volume Required	Minimum Volume	Stability
PREFERRED	Citrated Plasma	1mL	0.5mL	Frozen (-20C): 2 weeks Frozen (-80C): 6 months
ALTERNATIVE	-	-	-	-

REJECTION CRITERIA	Thawed in transit, refrozen or clotted sample
SPECIAL INSTRUCTIONS	This test in not appropriate for patients with prolonged aPTT results.

General Information

METHODOLOGY	Ratio, Clot-based
STAT TAT	< 48 hours (M-F)
STAT TAT Performance	> 90% of results released in 24 hours
ROUTINE TAT	< 1 week
ALTERNATIVE NAMES	APC Resistance, APCR, Resistance to Activated Protein C, Factor V Leiden screen, second generation APCR, R-APC
DESCRIPTION	Resistance of plasma to the anticoagulant effects of activated protein C (APC) leads to a hypercoagulable state and increased risk of deep vein thrombosis. This is an aPTT-based assay that measures the anticoagulant response in human plasma towards human activated protein C (APC). This is a second generation functional assay, making it more sensitive to Factor V Leiden mutations.
LIMITATIONS	The presence of anticoagulant medications, such as heparin, DOACs, or Vitamin K antagonist may interfere with APCR testing. This test is not appropriate for patients with prolonged aPTT results.
NORMAL RANGE	Ratio 2.0-3.5
ASSOCIATED TESTING	-
REFERENCES	1. Jorquera, JI et al. Modified test for activated protein C resistance. Lancet. 1994; 344:1162. 2. Trossaërt, M et al. The modified APC resistance test in the presence of factor V deficient plasma can be used in patients without oral anticoagulant. Thromb Haemost 1996; 75:521. 3. Heijmans BT et al. The risk of mortality and the factor V Leiden mutation in a population-based cohort. Thromb Haemost. 1998; 80:607-609.
SAMPLE REPORT	Upon request
NEW YORK STATE APPROVED	No

Test Codes

ORDER CODE	P3024
CPT CODE	85307
LOINC CODE	13590-5