Factor VIII Activity, Von Willebrand Factor Activity, Von Willebrand Antigen

1 to 3 days

Batched 1 to 2 times per week. Call 503-494-7383 if STAT.

See individual tests. 

Four full 2.7 mL LIGHT BLUE top tubes, 3.2% sodium citrate. Hemostasis & Thrombosis Lab sodium citrate specimens must be processed and frozen within 2 hours of specimen collection. Stability is 14 days at -70 C.

Draw volume is critical due to the liquid anticoagulant. Allow tubes to fill by vacuum.
• Tubes with rubber stopper: fill to line on label.
• Tubes with plastic (Hemogard) cap: the fill level is above the top of the label.
• Syringe: do not remove the vacutainer stopper. Insert the needle through the stopper and allow the tube to fill by vacuum. Do not overfill the vacutainer.
• Pediatric tubes have no vacuum. Remove the cap and add blood to the 1.3 mL mark. Do not overfill.

OHSU clinics must cab specimen to the Core Lab, Hatfield Research Center, 9th Floor (room 9D10) if processing is delayed or not possible on site. A phone call is helpful to alert the lab at 503-494-7383. 

Detailed specimen collection and processing instructions are located under Lab Sections and then the Hemostasis and Thrombosis (Opens in a new window) section.

For referral testing, submit four tubes, each with 1.0 mL frozen platelet poor citrated plasma.

Two full pediatric 1.3 mL LIGHT BLUE top tubes, 3.2% sodium citrate. Hemostasis & Thrombosis Lab sodium citrate specimens must be processed and frozen within 2 hours of specimen collection. Stability is 14 days at -70 C.

Prepare 3 aliquots:
FVIII: 500 microliters
vWF: 100 microliters
vWAg: 500 microliters

For pediatric patients requiring multiple coagulation tests, please call 503-494-7383 regarding draw volumes.

See individual tests.
For children less than 6 months, see link to published reference ranges (Opens in a new window).

This test is used in the diagnosis and classification of von Willebrand disease.

The von Willebrand factor (vWF) is absent or decreased in individuals with von Willebrand disease (vWD). vWF activity is the functional measure of the factor VIII molecule that is necessary for the agglutination of platelets observed in the presence of ristocetin. Since many variants of vWD exist, the yield of identifying patients with this disease is enhanced if all three of the following are assayed: factor VIII activity, von Willebrand factor antigen (vWF:Ag), and vWF-RCT activity. Because many patients with vWD have mild disease, repeated testing may be necessary to diagnose this disorder. Normal values do not exclude vWD. Female patients with vWD on oral contraceptives or who are pregnant may have normal values. Von Willebrand factor is also an acute-phase reactant and is elevated with stress or exercise.

Methodology: Refer to specific assays.

High doses of standard heparin (greater than 1.0 U/mL) may interfere with a PT mixing study. Anti-Xa agents such as Rivaroxaban may also interfere with PT mixing studies. Clinical correlation is advised.

Von Willebrand