Factor VIII Inhibitor by Bethesda Titer - Human

Profile or Test Panel
Method Clottable
Test Information Inhibitor to Factor VIII is screened for by mixing the test plasma with a known amount of Factor VIII. After a 2 hour incubation period at 37°C, the residual Factor VIII activity is determined in a factor VIII assay. By comparing the difference in the Factor VIII activity of the patient incubation mixture and a control mixture, the absence or presence of a Factor VIII inhibitor can be demonstrated. Some antibodies will only prolong the PTT after incubation (Ewing and Kasper, 1982).

Factor VIII inhibitors, IgG antibodies directed against factor VIII, can occur in alloimmunized patients with congenital factor VIII deficiency (Hemophilia A) or as autoantibodies. The latter are associated with pregnancy, autoimmune disease, or drugs but most often occur spontaneously, particularly among elderly persons.  Factor activity will be performed before testing for inhibitors.
Additional Test Information Normal Test Values:  None detected (values reported in Bethesda units)
Sample Requirements Whole Blood:  3.2% Sodium Citrated (blue top)  OR
Frozen Plasma
Requested Volume Two 5 ml 3.2 sodium citrated (blue top) tubes as whole blood  OR
Frozen plasma in 4 X 1mL aliquots in plastic tubes 
Minimum Volume or Pediatric volume Frozen Plasma:  at least 0.5ml in 2 plastic tubes.  
Sample Information Whole blood is preferred for testing but if it is not possible to send whole blood tubes TO ARRIVE HERE WITHIN 2 HOURS of collection then send frozen plasma.  To prepare plasma  centrifuge blue top tubes at 1500g for 15 minutes and remove the plasma and centrifuge a second time at 1500g for an additional 15 minutes.  Aliquot approximately 1 ml of plasma into 4 plastic tubes, and freeze.  
Shipping Information Whole Blood:  Send at ambient temperature (18-25C) and must be received within the lab in less than or equal to 3 hours after collection.
Frozen Plasma:  send on dry ice 

Send samples to:

Bloodworks Northwest
Attn: Hemostasis Laboratory
921 Terry Ave
Seattle, WA 98104

For additional information, please see Ordering Information
Requisition Form RFT- Hemostasis Reference Laboratory
Transaction Code 3220-02
CPT Codes 85335
Test Schedule Run twice a month
Report/ Results Fax number required to receive report