Factor VIII Activity, Clotting (FAC8)

LAB306

347

FAC8

1 mL frozen platelet-poor plasma collected in 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.

Note: Storage of whole blood at refrigerated temperatures prior to processing may lead to cryoprecipitate formation and falsely low Factor VIII and von Willebrand Factor studies.

Transport tube

Frozen

Room temperature: Unacceptable
Refrigerated: Unacceptable
Frozen: 30 days

Hemolysis • Received thawed

Monday, wednesday and friday

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.

50-180 % normal

This test is useful to evaluate a prolonged aPTT. The most common form of hemophilia is caused by a deficiency of Factor VIII. Hemophilia A is an X-linked disorder affecting between 1 in 5,000 to 10,000 males. Borderline low Factor VIII activity can be seen in female carriers of the defective Factor VIII gene. Typically this test is combined with other screening tests (eg. von Willebrand factor, Ristocetin Cofactor Activity) to evaluate for the presence von Willebrand disease.

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 (Thrombin Inhibitors): no effect to inhibitor pattern; Rivaroxaban, Apixaban, Edoxaban (Factor Xa Inhibitors): no effect to inhibitor pattern. Other limitations: Factor VIII levels may be falsely low due to Lupus anticoagulant. A chromogenic Factor VIII activity is suggested. The presence of factor VIII antibodies (autoantibodies or antibodies resulting from replacement therapy) can result in low factor VIII levels. This test is NOT recommended for patients receiving emicizumab (ie. Hemilbra) as this therapy will yield falsely elevated values. Factor VIII is a positive acute phase reactant and levels will increase in a variety of clinical scenerios.