Days Set Up
Thursday. Contact Special Coagulation lab if assay is needed on an urgent basis.
Analytic Time

8 hours

MiChart Code
Factor VIII Inhibitor Assay
Soft Order Code

Test Updated:


Bethesda Inhibitor
Factor 8 Inhibitor
Factor VIII Inhibitor Assay
Factor VIII:C Inhibitor Assay
Inhibitor Assay VIII

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All specimens should be accompanied by a requisition.

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MLabs provides all the supplies necessary for the collection of specimens.

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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.

Specimen Requirements

Collection Offsite

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.

Blue Top Tube
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)

Billing Information

CPT Code
Pro Fee Code

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Our High Standard

Quality that sets us apart

As the reference laboratory division of Michigan Medicine's Department of Pathology, MLabs shares the institution's commitment to applying established quality principles to clinical laboratory testing. Like other large organizations in complex, consequential fields, we rely on an established approach to monitor quality throughout the testing process.