Factor V Leiden
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Also called: Activated Protein C Resistance

In February1993, Dahlback published a case report of a middle-aged man with multiple venous thromboses who was resistant to the action of activated Protein C. With this report came the discovery of a major risk factor that is surprisingly prevalent. Since that time, it has been found that approximately ninety percent of activated protein C resistant patients have a mutant Factor V which is called Factor V Leiden .

The defect is a single amino acid substitution which results in the inability of protein C to degrade the mutant factor V (as it normally would). The end result is the loss of a major regulatory process and a tendency to hereditary venous thrombosis (called familial thrombophilia).

The incidence of Factor V Leiden in the general population is reported to be 3-7 % in patients of European descent and other reports indicate that the mutation has significant incidence across ethnic lines. Given such a high incidence, we should expect a significant number of test requests for Factor V Leiden .

The test is performed by extracting DNA from the white blood cells of blood collected in EDTA. The suspected mutant region is amplified by polymerase chain reaction (PCR) and the mutation is identified. Currently, the test is sent out and requires a written consult (with appropriate clinical indicators) and a full lavender top tube (3cc).

Pitfalls in asking for this test.
* It is not listed on any request slip.
* Few people have knowledge of the test.
* The written order looks a lot like a request for a Factor V assay (which is not the same thing and requires a different tube).

The bottom line?

Be on the lookout for this order. This is not the same as aFactor V assay which is rarely requested. Given the high incidence of mutation,Factor V Leiden should become a common request. Closely examine all orders for "Factor V" and remember to get a written consult and to collect a lavender top tube when Factor V Leiden is requested.

 

© 2004 Medical Center of Louisiana
Page updated: 9/24/04