Factor VIII Chromogenic Bethesda Profile, for Patients on Emicizumab

Clinical Use

Use

This assay is used to quantitate the titer of specific factor VIII antibodies in patients receiving emicizumab / Hemlibra®. Use of a standard, clot-based factor VIII test system will not accurately determine inhibitor titer due to interference from the therapeutic.

Special Instructions

Not provided.

Limitations

Hemolysis, lipemia, and icterus may interfere with this assay, leading to inaccurate results. Direct Xa inhibitors can cause erroneous low factor activity and false positive factor inhibitor results. Residual factor VIII activity, although limited by heat-inactivation of the sample, can falsely lower the Bethesda titer. Autoimmune inhibitors demonstrating second order kinetics may not be accurately measured by this system.

Test Details

Methodology

Other

Biomarkers

Factor VIII Activity

Analyte

Concentration / Level

Concentration / Level • Quantitative (Continuous) (e.g., copies/mL, % expression)

FVIII Chromogenic

Analyte

Concentration / Level

Concentration / Level • Quantitative (Continuous) (e.g., copies/mL, % expression)

LOINC Codes

Order Codes

3209-4 - Fact VIII Act/Nor PPP
49865-9 - Fact VIII Act/Nor PPP Chro
93450-5 - Fact VIII Inhib PPP Chro-aCnc

Result Codes

3209-4 - Fact VIII Act/Nor PPP
49865-9 - Fact VIII Act/Nor PPP Chro
93450-5 - Fact VIII Inhib PPP Chro-aCnc

Result Turnaround Time

5-10 days

Specimen

Plasma

Volume

2 mL

Minimum Volume

1 mL

Container

Blue-top (sodium citrate) tube

Collection Instructions

Citrated plasma samples should be collected by double centrifugation. Blood must be collected in a blue-top tube with 3.2% buffered sodium citrate. The tube must be filled completely to ensure a proper blood to anticoagulant ratio, and mixed immediately by gentle inversion at least six times.

Patient Preparation

The patient should not be anticoagulated. Do not draw from an arm with a heparin lock or heparinized catheter.

Storage Instructions

Freeze.

Causes for Rejection

Patients on therapy other than emicizumab. Any sample not being citrated plasma (3.2% sodium citrate). Samples showing signs of activation, or received thawed.