Sign in →

Test Code LAB3224 Factor VIII Inhibitor Evaluation

Additional Codes

Mayo Test Code: F8INH

Reporting Name

Factor 8 Inhib Prof

Useful For

Detecting the presence and titer of a specific factor inhibitor directed against coagulation factor VIII 

Profile Information

Test ID Reporting Name Available Separately Always Performed
F8A Coag Factor VIII Activity Assay, P Yes Yes

Reflex Tests

Test ID Reporting Name Available Separately Always Performed
IBETH Bethesda Units No No
F8IS Coag Factor VIII Assay Inhib Scrn,P No No
CCCR Special Coagulation Interpretation No No

Testing Algorithm

Testing begins with coagulation factor VIII activity assay with dilutions to evaluate assay inhibition; if the factor VIII activity assay is decreased, an inhibitor screen will be performed to look for specific factor VIII inhibition. If specific inhibition is apparent, the titer of the inhibitor will be determined.

Method Name

F8A: Activated Partial Thromboplastin Clot-Based Assay

F8IS, IBETH: Clot-Based Assay

Performing Laboratory

Mayo Medical Laboratories in Rochester

Specimen Type

Plasma Na Cit

Specimen Required

See Coagulation Studies in Special Instructions.


Specimen Type: Platelet-poor plasma

Collection Container/Tube: Light-blue top (citrate)

Submission Container/Tube: Plastic vials

Specimen Volume: 3 mL in 3 plastic vials each containing 1 mL

Collection Instructions:

1. Specimen must be drawn prior to factor replacement therapy.

2. Spin down, remove plasma, and spin plasma again.

3. Freeze specimens immediately at ≤-40 degrees C, if possible.

4. Send specimens in the same shipping container.

Additional Information:

1. Double-centrifuged specimen is critical for accurate results as platelet contamination may cause spurious results.

2. If priority specimen, mark request form, give reason, and request a call-back.

3. Each coagulation assay requested should have its own vial.

Specimen Minimum Volume

2 mL

Specimen Stability Information

Specimen Type Temperature Time
Plasma Na Cit Frozen 14 days

Reject Due To


Mild OK; Gross reject


Mild OK; Gross reject


Mild OK; Gross reject



Special Instructions

Reference Values


Adults: 55-200%

Normal, full-term newborn infants or healthy premature infants usually have normal or elevated factor VIII.*

*See Pediatric Hemostasis References in Coagulation Studies in Special Instructions.






0 Units

Day(s) and Time(s) Performed

Monday through Friday; Varies

CPT Code Information

85240-Factor VIII activity assay

85335-Bethesda titer (if appropriate)

85335-Factor VIII inhibitor screen (if appropriate)

85390-26-Special coagulation interpretation (if appropriate)

LOINC Code Information

Test ID Test Order Name Order LOINC Value
F8INH Factor 8 Inhib Prof 3209-4


Result ID Test Result Name Result LOINC Value
F8A Coag Factor VIII Activity Assay, P 3209-4

Test Classification

See Individual Test IDs