Factor II Inhibitor Profile, Comprehensive
Also known as: Bethesda Titer
Use
Confirmation and characterization of factor II inhibitor
Special Instructions
Not provided.
Limitations
If there is residual coagulation factor, it could falsely lower the result. The presence of direct Xa or thrombin inhibitor anticoagulant therapy may cause false-positive results. Lupus anticoagulant activity should be ruled out prior to assaying for factor inhibitors as this may cause false-positive titers. Individuals with lupus anticoagulant hypoprothrombinemia syndrome (LAHS) typically have low factor II levels but no measurable inhibitor titer, as the factor II antibody complex is rapidly cleared by the reticuloendothelial system. A negative factor II inhibitor profile, therefore, does not exclude a factor II inhibitor in individuals with a lupus anticoagulant. Autoimmune inhibitors cannot be accurately measured in the Bethesda titer system because of their second-order kinetics.6
Methodology
The factor II inhibitor (Bethesda titer) assay is performed using a prothrombin time-based system, using thromboplastin reagent.6 Serial dilutions are made of patient plasma with veronal buffered saline, then mixed with normal plasma containing close to 100% factor II activity, and are then incubated for two hours. A PT-based factor II assay using factor II-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 II inhibitor that neutralized 0.5 IU of factor II in this system. The number of serial dilutions tested is based on the anticipated level of the inhibitor.
Biomarkers
LOINC Codes
- 5902-2 - Prothrombin time
- 5959-2 - PT imm NP PPP
- 33356-7 - PT 1h NP Cont PPP
- 33884-8 - PT 1h NP Cont PPP Cont
- 14979-9 - aPTT PPP
- 3289-6 - Prothrom Act/Nor PPP
- 32635-5 - Fact II Inhib PPP-aCnc
Result Turnaround Time
3-5 days
Related Documents
For more information, please review the documents below
Specimen
Unknown
Volume
Not provided
Minimum Volume
Not provided
Patient Preparation
Ideally, the patient should not be on anticoagulant therapy. Avoid warfarin (Coumadin®) therapy for two weeks prior to the test and heparin, direct Xa and thrombin inhibitor therapies for about three days prior to testing. Do not draw from an arm with a heparin lock or heparinized catheter.
Other tests from different labs that may be relevant