Factor XI Activity, Clotting

*Take to processing ASAP

360

LAB309
 

1 mL frozen platelet-poor plasma collected in a 3.2% sodium citrate (light blue-top) tube

0.5 mL

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 tube

Frozen

Room temperature: Unacceptable
Refrigerated: Unacceptable
Frozen -20° C: 14 days
Frozen -70° C: 1 year

Hemolysis • Received thawed

Tues, thurs, sat

3-6 days

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.

65-150 % normal

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.