Factor XI Activity

Antihemophilic Factor C, Plasma Thromboplastin Antecedent (PTA)

7 days

Clot Formation

60-150%

Accredited NRL Laboratory

Once a week

Unexplained bleeding or excessive postoperative hemorrhage
• Prolonged PT or PTT requiring further investigation
• Suspected congenital factor deficiencies
• Liver disease evaluation affecting coagulation factor synthesis
• Monitoring replacement therapy in patients with known factor deficiencies

Plasma

2 mL

Sodium citrate (Light blue top), filled to the line

Ideally, the patient should not be on anticoagulation therapy. Avoid  heparin, direct Xa, and thrombin inhibitor therapies for about three days prior to testing. Do not draw from an arm with a heparin lock or heparinized catheter. Indicate and provide details if patient is on anticoagulant.

Plasma should be platelet free as possible. Platelet count should be less than 10 x 109/L
Double centrifugation:
Perform centrifugation for 15 mins at 2000-2500 g. Carefully remove 2/3 of plasma using a transfer pipette without disturbing the interface layer between plasma and cells. Transfer plasma to an aliquot tube and repeat the centrifugation step. Using a second pipette, separate plasma again into another aliquot tube, staying clear of the platelet layer at the bottom of the tube. Freeze immediately and maintain frozen until tested.