What is Factor V Leiden?
A. Factor V Leiden is a hereditary condition present in 15-20% of PE/DVT patients of European ancestry. A positive test for Factor V Leiden increases the risk of clots about three to four times compared to someone without it. In general, this risk is still small. However, if you are taking oral contraceptives and you have Factor V Leiden, the risk of a clot increases dramatically (about 35-fold). If you have Factor V Leiden, the risk of clots also increases with age. For Factor V Leiden patients who stop anticoagulant therapy after treatment, the risk for a second clot is about three times greater than for those without it.
