Factor 11 activity

Alphabetical Test listing

Factor 11 activity-13369

Factor 11 activity
Antihemophilic factor C
Factor XI activity
Plasma thromboplastin antecedent (PTA)

To evaluate isolated APTT prolongation and to document specific factor XI deficiency

  • Ideally, the patient should not be on anticoagulant therapy
  • Avoid warfarin (Coumadin®) therapy for two weeks prior to the test and heparin, direct Xa, and thrombin inhibitor therapies for about three days prior to testing
Sodium citrate (Na cit) plasma
1.0 mL
  • Do not draw from an arm with a heparin lock or heparinized catheter
  • Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate
  • Evacuated collection tubes must be filled to completion to ensure a proper blood-to-anticoagulant ratio
  • The sample should be mixed immediately by gentle inversion, at least six times, to ensure adequate mixing of the anticoagulant with the blood
  • A discard tube is not required prior to collection of coagulation samples unless the sample is collected using a winged (butterfly) collection system
    • With a winged blood collection set a discard tube should be drawn first to account for the dead space of the tubing and prevent under-filling of the evacuated tube
  • When noncitrate tubes are collected for other tests, collect sterile and nonadditive (red-top) tubes prior to citrate (blue-top) tubes.
    • Any tube containing an alternative anticoagulant should be collected after the blue-top tube
    • Gel-barrier tubes and serum tubes with clot initiators should also be collected after the citrate tubes
  • If the patient's hematocrit exceeds 55%, the volume of citrate in the collection tube must be adjusted
  1. Spin
  2. Transfer plasma to a Screw-cap polypropylene frozen transport vial/tube - 4mL (LabCorp), labelled as Na cit plasma, within two (2) hours of sample collection
  3. Freeze




  • Severe hemolysis
  • Improper labeling
  • Clotted specimen
  • Specimen diluted with I.V. fluids
  • Samples thawed in transit
  • Improper sample type
  • Sample out of stability
LabCorp Burlington (086314): R-LC
2 - 3 days

Factor XI activity is determined utilizing an aPTT-based one-stage clotting time assay. Factor XI-depleted plasma is used as the substrate and the clotting time with the patient plasma is compared to the clotting time of normal pooled plasma.


60 - 150%

Result 3226-8