Unit Code 9070:
Coagulation Factor VIII Activity Assay, Plasma

Diagnosing hemophilia A

Diagnosing vWD when measured with the vWF antigen and

ristocetin cofactor activity

Diagnosing acquired deficiency states

Investigation of prolonged activated partial thromboplastin time (APTT)

Activated Partial Thromboplastin Clot-Based Assay         
Not offered for detection of hemophilia carrier.
COAGULATION TESTING IS HIGHLY COMPLEX, OFTEN 
REQUIRING THE PERFORMANCE OF MULTIPLE ASSAYS AND 
CORRELATION WITH CLINICAL INFORMATION. FOR THAT
REASON, WE SUGGEST ORDERING "COAGULATION 
CONSULTATIONS".

Coag Factor VIII Activity Assay, P

F8A

Coagulation Factor VIII Activity Assay, Plasma

Factor VIII - Off hours order 399

Factor VIII Activity Assay

Hemophilia A

Soft-F8A

See "Coagulation Studies" in Special Instructions.

1. Draw blood in a light blue-top (citrate) tube(s). Spin down, remove

    plasma, spin plasma again, and place 1 mL of platelet-poor

    plasma in plastic vial. (Glass vial is not acceptable.)

   Note: Double-centrifuged specimen is critical for

             accurate results as platelet contamination may

             cause spurious results.

2. Freeze specimen immediately at < or =  -40 degrees C, if possible.

3. Send specimen frozen.

   Note: Each coagulation assay requested should have its

             own vial.

4. If priority specimen, mark requisition, give reason, and request a

    call-back.

Note:    If ordering electronically, no form is required with the specimen.

             If not ordering electronically, please complete and submit a

             "Coagulation Request Form" (Supply T237) with the specimen.

0.5 mL

Frozen\Refrig NO\Ambient NO

Hemolysis:                                          No

Lipemia:                                               No

Icteric:

Factor VIII is synthesized in the liver, and perhaps in other tissues.

It is a coagulation cofactor which circulates bound to von Willebrand

factor (vWF) and is part of the intrinsic coagulation pathway. The

biological half-life is 9-18 hours (average is 12 hours).

Congenital Factor VIII decrease is cause of hemophilia A which has

an incidence of 1 in 10,000 and is inherited in a recessive

sex-linked manner on the X chromosome. Severe deficiency (<1%)

characteristically demonstrates as hemarthrosis, deep tissue

bleeding, excessive bleeding with trauma and ecchymoses.

Factor VIII may be decreased in von Willebrand's disease (vWD).

Acquired deficiency states also occur.

Antibodies specific for Factor VIII are the most commonly occurring

specific inhibitors of coagulation factors and can produce serious

bleeding disorders (acquired hemophilia).

Factor VIII is highly susceptible to proteolytic inactivation,

with the potential for spuriously decreased assay results.

Adults:  55-205%

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.

See "Cautions”

Mild hemophilia A:  5-50%

Moderate hemophilia A:  1-5%

Severe hemophilia A:  <1%

Congenital deficiency may also occur in combined association with

Factor V deficiency.

Liver disease usually causes an increase of Factor VIII activity.

Acquired deficiencies of Factor VIII have been associated with

myeloproliferative or lymphoproliferative disorders (acquired vWD),

inhibitors of Factor VIII (autoantibodies, post-partum conditions,

etc.), and intravascular coagulation and fibrinolysis.

May be decreased with vWF in vWD.

Factor VIII is a labile protein. Improper handling of a specimen

may give a false result.              

Factor VIII is highly susceptible to proteolytic inactivation,

with the potential for spuriously decreased assay results. A

normal plasma specimen (processed in same fashion as for patient)

must accompany patient specimen. Normal results can be regarded

as reliable, but decreased result needs to be correlated with

other clinical and laboratory information. Repeat testing may be

necessary.

Factor VIII activity in frozen-thawed plasma specimens may be

10-20% lower than if assayed in fresh specimens, even under

optimum conditions of processing and transportation, or maybe

even lower if these conditions are suboptimal.

Factor VIII rises in response to a number of factors- pregnancy,

estrogen therapy, stress, disease, etc.

Not useful for inferring carrier status in suspected female

carriers of hemophilia A, unless it is below 50% of normal.

See "Specific Coagulation Factor Assay References" in Coagulation

Studies in Special Instructions.

Factor VIII is assayed using a factor-deficient substrate in the

APTT test. (Owen CA Jr,  Bowie EJW, Thompson JH Jr:  Diagnosis

of Bleeding Disorders. 2nd Edition.  Boston, MA, Little, Brown

and Company, 1975)

Monday through Friday; Varies a.m.

1 day

3 days

14 days

$230.20

This test was developed and its performance characteristics

determined by Laboratory Medicine and Pathology, Mayo Clinic.

This test has not been cleared or approved by the U.S. Food

and Drug Administration.

85240