Factor V inhibitor profile, comprehensive-994

Test info

Factor V inhibitor profile, comprehensive
Bethesda titer
  • Activated partial thromboplastin time (aPTT)
  • Factor V activity
  • Factor V Bethesda titer
  • Prothrombin time (PT)
  • PT 1:1 mix with normal plasma
  • PT 1:1 mix with saline

Confirmation and characterization of factor V inhibitor



The patient should not be on anticoagulant therapy

Sodium citrate (Na cit) plasma
6 mL (2 mL in each of three tubes)
  • Do not draw from an arm with a heparin lock or heparinized catheter
  • Immediatley following collection, mix sample thoroughly by gentle inverting 8 - 10 times, to prevent clotting
  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, cap, and recentifuge for 10 minutes.
  3. Use a second plastic pipette to remove plasma, staying clear of the platelets at the bottom of the tube.
  4. Transfer 2 mL of plasma into three (3) separate Screw-cap polypropylene frozen transport vial/tube - 4mL (LabCorp) labelled as Na cit plasma
  5. Freeze immediately

Frozen (preferred) – 30 days

Ambient – 4 hours

Refrigerated – NO


LabCorp Esoterix Coag Laboratory (500380): R – NX
Mo – Th, Sat
3 – 5 days

The factor V 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 V activity, and are then incubated for two hours. A PT-based factor V assay using factor V-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 V inhibitor that neutralized 0.5 IU of factor V in this system. The number of serial dilutions tested is based on the anticipated level of the inhibitor.

Clinical and Interpretive info


Prothrombin and APTT, sec

Factor V activity, % and Facator V inact assay, <0.8 Bethesda


85611 x 2