Factor XI Activity

Additional Info: 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.

Useful For: This test is useful to evaluate a prolonged aPTT. Deficiency of Factor XI is most common among those with Ashkenazi Jewish heritage.

Methodology: Photometric Clot Detection

Specimen Requirements:
1 blue-top (citrate) tube (minumum: the remaining platelet poor plasma separated from 2.7 mL whole blood). Centrifuge blue-top within 60 minutes of collection. Separate plasma and FREEZE immediately. Send specimen frozen in plastic vial. Do not refrigerate.

If using a butterfly collection set, fill a 1 mL waste tube prior to blue-top. This ensures full blood volume in blue-top.
Tube must be filled to capacity.
Draw specimen by vacuum. Do not overfill the tube.
Hemolyzed specimens are not acceptable.
If collecting multiple factor studies, draw each factor in separate tube.

Analytical Time: 3 days

Days Set Up: Monday through Friday

CPT Information:
85270 –