Test Directory

Patients with severe and moderate hemophilia often need specific substitution therapy with plasma derived or recombinant Factor VIII concentrates. About 15-35% of hemophiliacs treated with FVIII concentrates develop specific alloantibodies against human FVIII (inhibitors). The development of functionally inhibiting alloantibodies in hemophilia represents a serious clinical problem. In some patients, infusion of excessive amounts of Factor VIII may be utilized to overcome the antibody. However, this may result in an increased titer of the inhibitor leaving the patient unresponsive to further treatment. Therefore, detection and quantitation of inhibitors is of great importance in the care of these patients.

In non-hemophiliacs, development of circulating FVIII inhibitors can lead to acquired hemophilia, a rare bleeding disorder with an incidence of 1 per 106 persons per year. Acquired hemophilia can develop in patients with immunologic disorders such as rheumatoid arthritis, postpartum women, and in older individuals with no underlying disease.

Inhibitors to Factor VIII have been denoted as high- or low-responses based on the amnestic response of the antibody to antigenic challenge. Alloantibodies, which demonstrate an increase in titer, have been termed high-response inhibitors while those that do not have been termed low-response inhibitors. An antibody which is persistently 5 Bethesda units per mL (BU/mL) despite repeated challenge with substitution factor concentrate should be termed as low-response inhibitor, whereas the term high-response inhibitor should be applied to cases where the inhibitory activities have been >5 BU/mL at any time.

Factor VIII Activity and Factor VIII Inhibitor give a quantitative value for inhibitor activity in the determination of treatment options and the Nijmegen gives a more accurate value to low titer inhibitors which impacts treatment options.

Unlike other tests which use human coagulation Factors IX and X, the reagents used in this test contain bovine Factors IX and X. In patients being treated with Emicizumab (Hemlibra), the drug will interact with activated Factor IX and Factor X, which will result in Factor X being activated in the absence of Factor VIII activity. This could result in a false negative result, as even in the presence of Factor VIII inhibitors Emicizumab will cause the coagulation cascade to proceed. Emicizumab does not interact with bovine factors therefore there is no risk of Emicizumab interference with this test.

Specimen Type: Platelet-Poor Plasma

Collection Container: Light Blue Top (Sodium Citrate)

Desired Specimen Volume: 6 mL

1. Collect 3 light blue top (sodium citrate) tubes via venipuncture.
2. Fill entire tubes with whole blood.

Platelet-Poor Plasma Processing Instructions

1. Perform platelet-poor plasma processing procedure.
2. Transfer 2 mL of platelet-poor plasma into 3 separate clear aliquot tubes (screw cap) and freeze immediately.
3. Please submit a separate, frozen aliquot tube for each special coagulation assay ordered.

Transport to the laboratory frozen.

• Gross hemolysis
• Grossly lipemic
• Grossly icteric

See patient report.

• FVIII Bethesda Inhibitor
• Bethesda Assay with Nijmegen Mod