If factor activity level is less than 40%, an inhibitor test will be performed.

Routine: 1 Day
Urgent: N/A

Activities are batched daily 7 days a week. Inhibitors are batched twice per week.

2 to 2.7 mL blood in a LIGHT BLUE top tub, 3.2% sodium citrate.

3.2% sodium citrate tubes are acceptable when they are filled to the line on the manufacturers label. Tubes must be full (see comments below). For referral testing, submit 3 x 1.0 mL platelet poor plasma.

Sodium citrate specimens must be processed and frozen within 2 hours of specimen collection.

OHSU Clinics must cab specimens to the Core Lab, Hatfield Research Center (HRC), Room 9D05 if processing is delayed or not possible on site. A phone call is helpful to alert the lab at 503-494-5764.

Detailed instructions are under Hemostasis & Thrombosis section (Opens in a new window).

One 2.7 mL correctly filled in an adult size LIGHT BLUE top tube, or two correctly filled 1.3 mL pediatric BLUE top tubes, 3.2% sodium citrate.

A single 1.3 mL pediatric tube may be sent but will only allow for factor activity testing; the inhibitor, if indicated, may not be performed due to insufficient plasma volume.

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

Reference Range: 50% to 150%
Inhibitor: Less than 0.6 BU

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.

Avoid warfarin (Coumadin) therapy for two weeks and heparin therapy for 2 days prior to the test.

Assay to detect a circulating anticoagulant to factor VIII. Some patients with hemophilia A develop inhibitors to infused factor VIII, which may completely neutralize the action of the factor. In rare cases, individuals without hemophilia may also develop factor VIII inhibitors. For these patients, inhibitors result in spontaneous episodes of bleeding with no prior indication of any coagulation disorder. The action of the inhibitors differs somewhat between patients with hemophilia A and those without the disorder. Inhibitors in hemophiliacs tend to result in complete inactivation of factor VIII when enough inhibitors are present. In contrast, patients without hemophilia who develop inhibitors may still have some factor VIII activity even though the inhibitor is present. Simple vs. complex kinetics noted.

Methodology: Time-temperature dependent factor VIII assay (clotting Bethesda assay).

Factor 8
Inhibitor
FVIII