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Test Code LAB5076 Factor VIII Inhibitor Evaluation

Additional Codes

 

Test Name in EPIC EPIC Test Code Mnemonic Mayo Test ID
COAG FACTOR VIII INHIB SCREEN, PANEL LAB5076 CF8IN 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

Hemolysis

Mild OK; Gross reject

Lipemia

Mild OK; Gross reject

Icterus

Mild OK; Gross reject

Other

NA

Special Instructions

Reference Values

FACTOR VIII ACTIVITY ASSAY

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.

 

FACTOR VIII INHIBITOR SCREEN

Negative

 

BETHESDA TITER

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 In Process

 

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

Specimen Retention Time

See individual unit codes

Method Description

The factor VIII assay is performed on the Instrumentation Laboratory ACL TOP using the activated partial thromboplastin time (APTT) method and a factor deficient substrate. Patient plasma is combined and incubated with a factor VIII deficient substrate (normal plasma depleted of factor VIII by immunoadsorption) and an APTT reagent. After a specified incubation time, calcium is added to trigger the coagulation process in the mixture. At which time, the time to clot formation is measured optically using a wavelength of 671 nm.(Owen CA Jr, Bowie EJW, Thompson JH Jr: Diagnosis of Bleeding Disorders. 2nd edition. Boston, MA, Little, Brown and Company, 1975)

 

The factor VIII inhibitor screen consists of measuring the difference in factor VIII activity (partial thromboplastin time assay) before and after incubation of a mixture of normal plasma and patient's plasma for 1 hour at 37° C. For optimal sensitivity, the factor VIII value of the normal plasma is adjusted to approximately 20%, because the factor VIII assay is more sensitive in this area of the curve. In addition, an excess of patient's plasma will make the test more sensitive to small amounts of inhibitors.(Owen CA Jr, Bowie EJW, Thompson JH Jr: The Diagnosis of Bleeding Disorders. 2nd edition. Boston, MA, Little, Brown, and Company, 1975, pp 143-145)

 

If the inhibitor screen is positive for an inhibitor of factor VIII, the inhibitor will be quantitated by the Bethesda assay. In the Bethesda procedure, inhibitors are quantified by mixing equal volumes of serially diluted plasma with normal plasma. This mixture is incubated 2 hours at 37° C, and its factor VIII activity is measured and compared to a control run at the same time. The difference between the factor VIII activity of the patient's incubation mixture and that of the control is used to calculate the titer. The residual factor VIII activity is converted to Bethesda units: 50% residual factor VIII is equal to 1 Bethesda unit. Assays using the same basic principle as the Bethesda assay are used to quantitate the inhibitors of the other coagulation factors.(Kasper CK, Aldedort LM, Counts RB, et al: A more uniform measurement of factor VIII inhibitors. Thromb Diath Haemorrh 1975;34:869-872)

Analytic Time

2 days

Cautions

This test is not useful for detecting the presence of inhibitors directed against other clotting factors and will not detect the presence of lupus anticoagulants.

 

If presence or type of inhibitor is unknown, PROCT / Prolonged Clot Time Profile or LUPPR / Lupus Anticoagulant Profile should be ordered.

 

Occasionally, a potent lupus-like anticoagulant may cause false-positive results for a specific factor inhibitor (eg, factor VIII or IX). See preceding caution statement.

Clinical Information

Factor VIII inhibitors are IgG antibodies directed against coagulation FVIII that typically result in development of potentially life-threatening hemorrhage. These antibodies may develop in 1 of 4 different patient populations:

-Patients with congenital FVIII deficiency (hemophilia A) in response to therapeutic infusions of factor VIII concentrate

-Elderly nonhemophiliac patients (not previously factor VIII deficient)

-Women in postpartum period

-Patients with other autoimmune illnesses

Interpretation

Normally, there is no inhibitor, (ie, negative result).

 

If the screening assays indicate the presence of an inhibitor, it will be quantitated and reported in Bethesda (or equivalent) units.

Test Classification

See Individual Test IDs