Days Set Up
Analytic Time

4 hours

MiChart Code
Factor IX Inhibitor Assay
Soft Order Code

Test Updated:


Bethesda Inhibitor
Factor 9 Inhibitor
Factor IX Inhibitor Assay
Factor IX:C Inhibitor Assay
Inhibitor Assay IX

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Test Overview

Test Methodology

Bethesda Assay

Test Usage

Routine comprehensive evaluation of patients with severe hemophilia. Evaluation of increased bleeding problems in patients with hemophilia.

Reference Range

The Factor IX inhibitor level in a normal individual is <0.5 Bethesda units. 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

The Factor 9 assay activity level is included in this test order. The inhibitor level will not be performed if the factor activity level is greater than 50%.Collect specimen in two blue top (citrate 3.2%) tubes. Mix by inversion. Specimen should arrive at lab within 3 hours of collection; transport at room temperature. Alternatively, centrifuge, aliquot plasma from each blue top tube into separate polypropylene plastic vials, 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.