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Specimen Collection Manual and Test Catalog

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FACTOR INHIBITOR TITER (BETHESDA ASSAY)

Geisinger Epic Procedure Code:  LAB2252    Geisinger Epic ID:  14940

SPECIMEN COLLECTION
Specimen type: 

Platelet-free plasma


Preferred collection container: 
Alternate collection container: 
Other size blue-top (3.2% sodium citrate) tubes (e.g., 1.8 mL, 4.5 mL)
Specimen required: 

4 (Four) 1.0 mL plasma aliquots for a single study. Samples requiring heparin neutralization require an additional 0.5 mL for each test.


Special notes: 
  • Ideally the patient should not be receiving anticoagulant medication as it may interfere with testing and cause erroneous results. See Anticoagulation Impact on Coagulation Tests.
  • If the patient’s hematocrit (HCT) is >55%, the volume of anticoagulant in the tube should be adjusted. Contact a performing location for special tube preparation to reduce the citrate in the collection tube. For those patients with HCT >65.4% see LAB3632 Stago Sodium Citrate Adjustment Chart for formula to determine amount of citrate removal required.
  • When possible, use fresh venipuncture to collect blood to avoid activation of coagulation by tissue thromboplastin. Blood may be drawn from an indwelling catheter or vascular access device. Draw sample from a lumen that has not been heparinized or flush the line with 5 ml of saline, and discard or use for other purposes the first 5-10 mL of blood.
  • Tubes should be >90% filled.
  • Immediately mix gently after collection by inverting the tube end over end 5 to 6 times. Avoid vigorous mixing or additional inversion. Observe for the presence of clots. Recollect if fibrin clots observed.
  • Transport at ambient temperature to processing location and processing should be completed within 4 hours.
  • Butterfly device collections, draw a discard tube first to remove air from collection tubing.


SPECIMEN PROCESSING
Processing instructions: 

Centrifuge as soon as possible (within 60 minutes) at designated speed and time to obtain platelet-poor plasma (< 10,000/uL). Remove plasma and re-spin the plasma for 10 minutes at 3000 rpm and submit four (4) 1.0-1.9 ml platelet free plasma aliquots.

For a single NaCit blue top tube collection, create 1 aliquot NaCit and if additional plasma remains, create an additional aliquot NaCit. If multiple tubes collected, create 1 aliquot NaCit for each NaCIt blue top tube collected plus one additional aliquot NaCit. Aliquots should be 1.0-1.9 mL and all plasma-based coagulation tests must be moved to aliquot(s).


Transport temperature: 

Frozen.


Specimen stability: 

Frozen: -20°C for 30 days, -70°C for 6 months. Room temperature: 4 hours.


Rejection criteria: 

Clotted specimen. Stability exceeded. Overfilled or underfilled tubes. HCT > 55% and anticoagulant ratio not adjusted. Note: Specimen suspected of thawing in transport, indicated by slant in aliquot or specimen in lid of tube, will have testing performed, and the comment “interpret results with caution as thawing suspected” added to results.



TEST DETAILS
Reference interval: 

See sendout reference laboratory.


CPT code(s):  85335
Note: The billing party has sole responsibility for CPT coding.  Any questions regarding coding should be directed to the payer being billed.
The CPT codes provided by GML are based on AMA guidelines and are for informational purposes only.

Test includes: 

Inhibitor titer for specific factor.


Methodology: 
Functional mechanical clot-based
Synonyms: 

Inhibitor for specific factor, FAIT, Antibody against coagulation factor, Bethesda titer


Clinical significance: 

The factor inhibitor titer test is used to quantitate the level of a possible factor inhibitory antibody in a plasma sample. It is typically used to quantify Factor VIII and IX inhibitors, but it can be used with other coagulation factors. It should be considered when a mixing study shows an inhibitor is present with low factor activity.


Doctoral Director(s): 
Michelle Grant DO
Review Date:  09/03/2026

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