Test Catalog

Test ID: 8INHE    
Factor VIII Inhibitor Evaluation, Plasma

Useful For Suggests clinical disorders or settings where the test may be helpful

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


This test is not useful for the detection of a lupus-like circulating anticoagulant inhibitor, a nonspecific circulating anticoagulant, or other inhibitors that are not specific for coagulation factors.

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

Testing begins with coagulation factor VIII activity assay with dilutions to evaluate assay inhibition; if the factor VIII activity assay is normal or increased, a technical interpretation will be provided. If the factor VIII activity assay is decreased, an inhibitor screen will be performed at an additional charge to look for specific factor VIII inhibition and a professional interpretation will be provided. If specific inhibition is apparent, the titer of the inhibitor will be determined.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Factor VIII (FVIII) 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 non-hemophiliac patients (not previously factor VIII deficient)

-Women in postpartum period

-Patients with other autoimmune illnesses

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.


Adults: 55-200%

Normal, full-term newborn infants or healthy premature infants typically have levels greater or equal to 40%.*

*See Pediatric Hemostasis References in Coagulation Guidelines for Specimen Handling and Processing in Special Instructions.

Interpretation Provides information to assist in interpretation of the test results

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.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

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

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Kasper CK: Treatment of factor VIII inhibitors. Prog Hemost Thromb. 1989;9:57-86

2. Peerschke EI, Castellone DD, Ledford-Kraemer M, et al: Laboratory assessment of FVIII inhibitor titer. Am J Clin Pathol. 2009;131(4):552-558. doi: 10.1309/AJCPMKP94CODILWS

3. Pruthi RK, Nichols WL: Autoimmune factor VIII inhibitors. Curr Opin Hematol. 1999;6(5):314-322. doi: 10.1097/00062752

4. Kottke-Marchant. K, ed. Laboratory Hematology Practice. Wiley Blackwell Publishing; 2012

Special Instructions Library of PDFs including pertinent information and forms related to the test