F5IS - Performance: Coagulation Factor V Inhibitor Screen, Plasma

Test Catalog

Test Name

Test ID: F5IS    
Coagulation Factor V Inhibitor Screen, Plasma

Method Description Describes how the test is performed and provides a method-specific reference

This assay consists of measuring the difference in factor V activity (prothrombin time assay) before and after incubation of a mixture of normal plasma and patient's plasma for 1 hour at 37 degrees C. For optimal sensitivity, the factor V value of the normal plasma is adjusted to approximately 20%, because the factor V 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 V, the inhibitor will be quantitated by the "Bethesda assays." 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 degrees C, and its factor V activity is measured and compared to a control run at the same time. The difference between the factor V activity of the patient's incubation mixture and that of the control is used to calculate titer. The residual factor V activity is converted to "Bethesda units": 50% residual factor V is equal to 1 Bethesda unit.(Kasper CK, Aldedort LM, Counts RB, et al: A more uniform measurement of factor VIII inhibitors. Thromb Diath Haemorrh 1975;34:869-872)

PDF Report Indicates whether the report includes an additional document with charts, images or other enriched information


Day(s) and Time(s) Test Performed Outlines the days and times the test is performed. This field reflects the day and time the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time required before the test is performed. Some tests are listed as continuously performed, which means assays are performed several times during the day.

Monday through Friday

Analytic Time Defines the amount of time it takes the laboratory to setup and perform the test. This is defined in number of days. The shortest interval of time expressed is "same day/1 day," which means the results may be available the same day that the sample is received in the testing laboratory. One day means results are available 1 day after the sample is received in the laboratory.

1 day

Maximum Laboratory Time Defines the maximum time from specimen receipt at Mayo Medical Laboratories until the release of the test result

3 days

Specimen Retention Time Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded

Until reported

Performing Laboratory Location The location of the laboratory that performs the test