Bethesda Assay for Factor 8


Abbrev Code:BETH2   
Order Code:LAB3317Order Name:Bethesda for Factor 8
Synonyms:Factor 8 Hemophilia Antibody; Factor 8 Inhibitor; Hemophilia A Inhibitor; Bethesda Assay for Factor VIII
Methodology:Measurement of residual Factor 8 on mixtures of patient plasma mixed with normal pooled plasma. Factor 8 Bethesda samples are incubated for 2 hours at 37 C.
CPT Codes: 85335 x1, 85335 x1
Turnaround Time:Specimen is accepted and processed 24 hours/day, 7 days/week. Test is performed as needed; results are reported within 2-4 days.
Special Instructions:Indicate on request form when the last Factor 8 infusion was administered. If Thrombin Time is >60 seconds. Bethesda Assay for Factor 8 will be cancelled with the following comment: SPECIMEN CANCELLED, INTERFERING SUBSTANCES DETECTED. CORRELATION WITH MEDICATIONS RECOMMENDED.
Associated Links:

Specimen Collection and Processing for Coagulation Specimens



Collection Instructions

Specimen:Blood
Optimal Volume:Three 3 mL tubes, each containing 2.7 mL blood; each filled to fill line on tube.
Minimum\Peds Volume:Two 3 mL tubes, each containing 2.7 mL blood; each filled to fill line on tube.
Container:THREE Blue Na Citrate, 3.2% - fill to fill line on tube
Collection Instructions:See link to Specimen Collection and Processing of Coagulation Specimens.
Causes for Rejection:Underfilled tubes, overfilled tubes, clotted specimens, not received or processed and frozen within 4 hours of collection or, specimen thawed during transit. Patients on Hemlibra® (emicizumab)
Contraindications:Factor 8 infusion within last week


Processing and Shipping

Specimen Processing:
  • Process for Platelet Poor Plasma within 4 hours of collection.
  • Aliquot plasma, place clear tape around label, and freeze at -20C or on dry ice within 4 hours of collection.
  • If multiple tests are collected on 1 blue top, split each blue top into 2 aliquots. Minimum 0.5 mL per tube.
  • A maximum of 6 aliquots are needed per collection.
     
See link to Specimen Collection and Processing for Coagulation Specimens.
Shipping Instructions:
  • Ensure specimen is frozen before shipping.
  • Ship on dry ice, sample must remain frozen during shipping.
     
See link to Specimen Collection and Processing for Coagulation Specimens.
Test Performed at or Referral Lab UM Special Coag (K)  (UMMC East Bank)


Interpretive

Reference Range:0 Bethesda U/mL
Use:The Bethesda assay is designed specifically to measure the concentration of anti-Factor 8 antibody in patients with hemophilia A. One Bethesda Unit is the amount of antibody that will inactivate 0.5 U/mL (50%) of Factor 8. Patients with "spontaneous" (acquired) antibodies will give variable results because of the unique conditions of the test and the nature of these types of antibodies.


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