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.

Test Limitations

Test will not be performed if Factor IX level is above 50%.

Test Details
Days Set Up
Thursday, starting at 8am.
Analytic Time

4 hours

Soft Order Code
MiChart Code
Factor IX Inhibitor Assay
  • Bethesda Inhibitor
  • Factor 9 Inhibitor
  • Factor IX Inhibitor Assay
  • Factor IX:C Inhibitor Assay
  • Inhibitor Assay IX
  • INHIB9
  • INH9
STAT Availability

Please contact special coagulation lab.

Specimen Requirements
Collection Instructions

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.

Test is not indicated if Factor IX level is greater than 50%,the 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 IX inhibitors occur most commonly in patients with severe x-linked recessive deficiencies of factor IX activity and may compromise the care of these patients severely.

CPT Code
Fee Code