Test Overview
Test Methodology

Nijmegen Bethesda Assay

Test Usage

Evaluation of increased bleeding problems in patients with hemophilia or abrupt-onset bleeding distress in postpartum women, patient with collagen vascular disorders, or elderly individuals. Assay is suitable for both treated and untreated patients.

Reference Range *

The Factor VIII inhibitor level in a normal individual is less than 0.5 Bethesda unit. Critical value: greater than 0.5 Bethesda unit (if no prior inhibitor present).

* Reference ranges may change over time. Please refer to the original patient report when evaluating results.

Test Limitations

Patients receiving Hemlibra will need to be tested using chromogenic methods. Please notify the special coagulation laboratory at 936-5316 when a patient is receiving Hemlibra.

Test Details
Days Set Up
Thursday, starting at 8am. Contact Special Coagulation lab if assay is needed on an urgent basis.
Analytic Time

8 hours

Soft Order Code
MiChart Code
Factor VIII Inhibitor Assay
  • Bethesda Inhibitor
  • Factor 8 Inhibitor
  • Factor VIII Inhibitor Assay
  • Factor VIII:C Inhibitor Assay
  • Inhibitor Assay VIII
  • INHIB8
  • INH8
STAT Availability

Contact Special Coagulation lab if assay is needed on an urgent basis.

Specimen Requirements
Collection Instructions

MLabs recommends performing or ordering a Factor VIII Assay activity level prior to ordering the Factor VIII Inhibitor Assay because the Inhibitor Assay will not be performed if the Factor VIII level is greater than 50%. A Factor VIII level is included in the order for the Factor VIII Inhibitor Assay. Collect specimen in a blue top (citrate 3.2%) tube. Mix by inversion. Specimen should arrive at lab within 3 hours of collection; transport at room temperature. Alternatively, centrifuge, aliquot plasma into a plastic vial, and freeze the specimen within 4 hours of collection. Transport frozen specimen on dry ice. Collection of the blood through lines that have been previously flushed with heparin should be avoided. If the blood must be drawn through a VAD (vascular access device), the line should be flushed with 5 mL of saline and the first 5 mL of blood or six dead space volumes of the VAD discarded.

Test is not indicated if Factor VIII level is greater than 50%,if patient is receiving anticoagulation therapy, or if the patient is receiving factor replacement therapy.
Normal Volume
2 full 2.7mL tubes or 2mL of plasma (two 1mL aliquots)
Minimum Volume
2 full 1.8mL tubes or 2mL of plasma (two 1mL aliquots)
Storage Temperature
Room temperature for whole blood or frozen aliquot of citrated plasma.
Rejection Criteria
Specimens will be rejected if not properly filled, clotted, grossly hemolyzed, or contaminated with heparin.
Additional Information

Factor VIII inhibitors occur most commonly in patients with severe x-linked recessive deficiencies of factor VIII activity and may compromise the care of these patients severely. Factor VIII inhibitors also may occur spontaneously in previously normal individuals, most commonly elderly individuals, postpartum women, or patients with collagen vascular disease, and may represent, a life-threatening manifestation of an immune dyscrasia. Bleeding associated with such inhibitors is usually abrupt in onset and severe, necessitating rapid detection of the inhibitor and appropriate treatment.

CPT Code
Fee Code