Factor VIII inhibitor profile, comprehensive-994

Test info

  
Factor VIII inhibitor profile, comprehensive
  
994
  
LAB994
  
MSO
  
Bethesda Titer
  
Activated partial thromboplastin time (aPTT)
aPTT 1:1 mix with normal plasma
aPTT 1:1 incubated mix with normal plasma
aPTT 1:1 mix with saline
Factor VIII activity
Factor VIII Bethesda titer
  

Confirmation and characterization of factor VIII 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 always be accurately measured in the Bethesda titer system.

Specimen

  

The patient should not be anticoagulated

  
Sodium citrate (Na cit) plasma
  
  
3.0 mL
  
  • Do not draw from an arm with a heparin lock or heparinized catheter.
  
  
  1. Centrifuge for 10 minutes and carefully remove 2/3 of the plasma using a plastic transfer pipette, being careful not to disturb the cells.
  2. Deliver to a plastic transport tube and cap tightly
  3. Recentifuge for 10 minutes.
  4. Use a second plastic pipette to remove plasma, staying clear of the platelets at the bottom of the tube.
  5. Transfer the plasma into a Screw-cap polypropylene frozen transport vial/tube - 4mL (LabCorp), labelled as Na cit plasma
  6. Freeze immediately.
  

Frozen (strict)

Refrigerated - NO

Ambient - NO

Performance

  
LabCorp (117157): R-NX
  
Mo - Fr
  
4 days
  

The factor VIII inhibitor (Bethesda titer) assay is performed using an activated partial thromboplastin time (aPTT)-based test system.6 Serial dilutions are made of patient plasma with veronal buffered saline, then mixed with normal plasma containing close to 100% factor VIII activity and are then incubated for one hour. An aPTT-based factor VIII assay using factor VIII-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 VIII inhibitor that neutralized 0.5 IU of factor VIII in this system. The number of serial dilutions tested is based on the anticipated level of the inhibitor.

Clinical and Interpretive info

  
aPTT 22.9 − 30.2 sec
aPTT 1:1 Normal plasma 22.9 − 30.2 sec
aPTT 1:1 Mix saline Not established
aPTT 1:1 NP mix, 60 min incub 22.9 − 30.2 sec
Factor VIII Activity 57 − 163 %

Billing

  
85240
85730
85732 x 3
  
Yes
  

Tracking

  
01/12/2022
  
12/21/2023