Factor 9 inhibitor
Factor 9 inhibitor-994
Factor IX inhibitor
- Factor IX activity
- Factor IX Bethesda titer
- Bethesda titer is not indicated and is cancelled if the factor activity is >40%.
Confirmation and characterization of factor IX inhibitor
If there is residual coagulation factor activity, it could falsely lower the Bethesda titer result. Lupus anticoagulant activity and antithrombotic agents that function as inhibitors should be ruled out prior to assaying for factor inhibitors in order to avoid factitiously positive results. Some inhibitors may fully neutralize factors in less than two hours. Autoimmune inhibitors that demonstrate second order kinetics cannot be accurately measured in the Bethesda titer system.
The patient should not be anticoagulated
- Do not draw from an arm with a heparin lock or heparinized catheter.
- If the patient's hematocrit exceeds 55%, the volume of citrate in the collection tube must be adjusted.
- Immediatley following collection, mix sample thoroughly by gentle inverting 8 - 10 times, to prevent clotting
- Centrifuge for 10 minutes and carefully remove 2/3 of the plasma using a plastic transfer pipette, being careful not to disturb the cells.
- Deliver to a plastic transport tube, cap, and recentifuge for 10 minutes.
- Use a second plastic pipette to remove plasma, staying clear of the platelets at the bottom of the tube.
- Transfer 4mL of plasma into two tubes (2 mL each). Use Screw-cap polypropylene frozen transport vial/tube - 4mL (LabCorp), labelled as Na cit plasma
- Freeze immediately
Frozen
Activated partial thromboplastin time (aPTT)-based system. Serial dilutions are made of patient plasma with veronal buffered saline, then mixed with normal plasma containing close to 100% factor IX activity and are then incubated for 2 hours. An aPTT-based factor IX assay using factor IX-depleted plasma substrate is then performed on these incubated mixtures. Results are compared to those of incubated normal plasma. One Bethesda unit is defined as the amount of factor IX inhibitor that neutralized 0.5 IU of factor IX in this system. The number of serial dilutions tested is based on the anticipated level of the inhibitor.
An interpretive report will be provided
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