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Factor XI Activity, Clotting
Test Code360
CPT Codes
85270
Preferred Specimen
1 mL platelet-poor plasma collected in a 3.2% sodium citrate (light blue-top) tube
Minimum Volume
0.5 mL
Instructions
Platelet-poor plasma: Centrifuge light blue-top tube for 15 minutes at approximately 1500 g within 60 minutes of collection. Using a plastic pipette, remove plasma, taking care to avoid the WBC/platelet buffy layer and place into a plastic vial. Centrifuge a second time and transfer platelet-poor plasma into a new plastic vial. Plasma must be free of platelets (<10,000/mcL). Freeze immediately and ship on dry ice.
Transport Temperature
Frozen
Specimen Stability
Room temperature: Unacceptable
Refrigerated: Unacceptable
Frozen -20°C: 14 days
Frozen -70°C: 1 year
Refrigerated: Unacceptable
Frozen -20°C: 14 days
Frozen -70°C: 1 year
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Hemolysis • Received thawed
Methodology
Clot Detection
Setup Schedule
Set up: Mon-Fri; Report available: Next day
Limitations
Expected impact by therapeutic levels (potential interference depends upon drug concentration): Warfarin: no effect; Heparin (UFH or LMWH): no effect to inhibitor pattern; Dabigatran or Argatroban (Thrombin Inhibitors): no effect to inhibitor pattern; Rivaroxaban or Apixaban (Factor Xa Inhibitors): no effect to inhibitor pattern.
Reference Range
65-150 % normal
Clinical Significance
This test is useful to evaluate a prolonged aPTT. Deficiency Factor XI is most common among those with Ashkenazi Jewish heritage. It should be noted that the risk for clinical bleeding does not correlate with the degree of deficiency. Occasionally patients with decreased Factor XI activity may show an inhibitor pattern on testing. This may be due to a lupus anticoagulant, a factor specific inhibitor, or a specific Factor XI inhibitor. The possibilities can be evaluated by mixing studies and/or specific testing for a lupus anticoagulant.
Anticoagulant interference: Expected impact by therapeutic levels (potential interference depends upon drug concentration): Warfarin: no effect; Heparin (UFH or LMWH): no effect to inhibitor pattern; Dabigatran or Argatroban (Direct Thrombin Inhibitors): no effect to inhibitor pattern; Rivaroxaban or Apixaban (Factor Xa Inhibitors): no effect to inhibitor pattern. Because of the possibility of falsely low levels, these drugs should be avoided, if not clinically contraindicated, for approximately 2-3 days before testing.
Anticoagulant interference: Expected impact by therapeutic levels (potential interference depends upon drug concentration): Warfarin: no effect; Heparin (UFH or LMWH): no effect to inhibitor pattern; Dabigatran or Argatroban (Direct Thrombin Inhibitors): no effect to inhibitor pattern; Rivaroxaban or Apixaban (Factor Xa Inhibitors): no effect to inhibitor pattern. Because of the possibility of falsely low levels, these drugs should be avoided, if not clinically contraindicated, for approximately 2-3 days before testing.
