Factor VIII inhibitor profile, comprehensive

Alphabetical Test listing

Factor VIII inhibitor profile, comprehensive-994

Factor VIII inhibitor profile, comprehensive
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.


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

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.

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 %
85732 x 3