Test Details
Methodology
The Nijmegen modification of the classic Bethesda inhibitor titration assay is used in a chromogenic factor VIII activity setting. Patient sample is heat-inactivated and clarified, then a serial dilution series is prepared in buffered normal plasma containing bovine serum albumin. A chromogenic factor activity is measured to determine residual activity and the inhibitor concentration is determined using an equation that relates the log % residual activity to inhibitor titer.
Result Turnaround Time
5 - 10 days
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
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
Testing is performed at Esoterix Coagulation Laboratory (UY No. 301676).
For use in the confirmation and characterization of factor VIII inhibitors for patients on emicizumab therapy. Not intended for use with any other therapeutic.
Limitations
Hemolysis, lipemia and icterus may interfere with this assay. Certain anticoagulant drugs (direct Xa inhibitors) may lead to an erroneously low factor activity and erroneously positive specific factor inhibitor results. Residual factor VIII activity could falsely lower the Bethesda titer although this is limited by heat-inactivation of the patient sample. Autoimmune inhibitors that demonstrate second order kinetics cannot always be accurately measured in the Bethesda titer system.
Specimen Requirements
Specimen
Citrated plasma, frozen
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 should be collected in a blue-top tube containing 3.2% buffered sodium citrate.1 Evacuated collection tubes must be filled to completion to ensure a proper blood to anticoagulant ratio.2,3 The sample should be mixed immediately by gentle inversion at least six times to ensure adequate mixing of the anticoagulant with the blood. A discard tube is not required prior to collection of coagulation samples, except when using a winged blood collection device (ie, "butterfly"), in which case a discard tube should be used.4,5 When noncitrate tubes are collected for other tests, collect sterile and nonadditive (red-top) tubes prior to citrate (blue-top) tubes. Any tube containing an alternate anticoagulant should be collected after the blue-top tube. Gel-barrier tubes and serum tubes with clot initiators should also be collected after the citrate tubes. Centrifuge for 10 minutes. Use a second plastic pipette to remove the plasma, staying clear of the platelets at the bottom of the tube. Transfer the plasma into a Labcorp PP transpak frozen purple tube with screw cap (Labcorp No. 49482). Freeze immediately and maintain frozen until tested.
Please print and use the Volume Guide for Coagulation Testing to ensure proper draw volume.
Stability Requirements
Temperature | Period |
|---|---|
Frozen | 12 months |
Freeze/thaw cycles | Stable x5 |
Storage Instructions
Freeze.
Patient Preparation
The patient should not be anticoagulated. Do not draw from an arm with a heparin lock or heparinized catheter.
Causes for Rejection
Patients on any therapy other than emicizumab therapy. Any sample other than citrated plasma (3.2% sodium citrate). Samples showing signs of activation, including the presence of fibrin clots, or received thawed.
References
Footnotes
LOINC® Map
| Order Code | Order Code Name | Order Loinc | Result Code | Result Code Name | UofM | Result LOINC |
|---|---|---|---|---|---|---|
| 504722 | Emicizumab FVIII Inhib Panel | 500666 | Factor VIII Activity | % | 3209-4 | |
| 504722 | Emicizumab FVIII Inhib Panel | 500193 | FVIII Chromogenic | % | 49865-9 | |
| 504722 | Emicizumab FVIII Inhib Panel | 504800 | FVIII Chrom Nijmegen Bethesda | CBU/mL | 93450-5 | |
| Order Code | 504722 | |||||
| Order Code Name | Emicizumab FVIII Inhib Panel | |||||
| Order Loinc | ||||||
| Result Code | 500666 | |||||
| Result Code Name | Factor VIII Activity | |||||
| UofM | % | |||||
| Result LOINC | 3209-4 | |||||
| Order Code | 504722 | |||||
| Order Code Name | Emicizumab FVIII Inhib Panel | |||||
| Order Loinc | ||||||
| Result Code | 500193 | |||||
| Result Code Name | FVIII Chromogenic | |||||
| UofM | % | |||||
| Result LOINC | 49865-9 | |||||
| Order Code | 504722 | |||||
| Order Code Name | Emicizumab FVIII Inhib Panel | |||||
| Order Loinc | ||||||
| Result Code | 504800 | |||||
| Result Code Name | FVIII Chrom Nijmegen Bethesda | |||||
| UofM | CBU/mL | |||||
| Result LOINC | 93450-5 |