Test Catalog

Test ID: F5IS    
Coagulation Factor V Inhibitor Screen, Plasma

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

Detection and quantitation of inhibitors against coagulation factor V


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 V activity assay with dilutions to evaluate assay inhibition; if the factor V activity assay is normal or increased, the inhibitor screen will be cancelled.  If the factor V activity assay is decreased, an inhibitor screen will be performed to look for specific factor V inhibition. 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 V inhibitors can occur in patients with congenital factor V deficiency after transfusion of fresh frozen plasma, however, more commonly, they occur spontaneously in previously healthy older patients who have no underlying diseases. Topical bovine thrombin or fibrin glue, which contain bovine thrombin and factor V, are commonly used in surgery for topical hemostasis and can result in development of anti-bovine thrombin/factor V inhibitors that cross-react with human thrombin and factor V. Other associations include antibiotics, transfusions and malignancies.

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: 75-165%

Normal, full-term newborn infants may have borderline low or mildly decreased levels (> or =30-35%) which reach adult levels within 21 days postnatal.*

Healthy premature infants (30-36 weeks gestation) may have borderline low or mildly decreased levels.*

*See Pediatric Hemostasis References section 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 testing for a specific factor inhibitor (eg, factor VIII or IX); see Advisory Information.

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

1. Hematology: Basic Principles and Practice. Seventh Edition. Edited by R Hoffman, EJ Benz Jr, LE Silberstein, et al. Elsevier, 2018

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

3. Laboratory Hematology Practice. Edited by K Kottke-Marchant. Wiley Blackwell Publishing, 2012

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