Factor V Leiden Test: Why Is This Test Important

Some of us may have heard of Factor V Leiden and know what this is all about. On the other hand, others may not be so sure. If you are among those who know what this is, keep reading for the amusement factor. However, if you are among those who think that Factor V Leiden is a pianist from the 19th century, keep reading. You need to know better!

Perhaps the best approach to talk about the Factor V Leiden Test and its importance is from the very basics. Let’s start with thrombophilia and build from there.

What is thrombophilia?

Thrombophilia is defined as an increased tendency to form abnormal blood clots that can block blood vessels. Think of it this way: people with thrombophilia have thicker blood than your average person that can clot much easier. A blood clot is actually the body’s repair mechanism to repair damage to either an artery or a vein. It is an accumulation of platelets (tiny blood cells) in the blood to stop bleeding. However, a clot is a blockage of the blood flow in the body and that is not a good thing. So, while blood clots are inherently protective, the outcome is negative and even painful. Thrombophilia is a genetic disorder that is caused by a mutation, which is where Factor V Leiden comes into play.

Factor V Leiden

Factor V Leiden is the name of a specific gene mutation that causes thrombophilia. It is also the most common inherited form of thrombophilia. Anywhere from 3% to 8% of Europeans have one copy of the mutation and an estimated one in every 5,000 people have two copies. People who have the mutation are at a much higher risk of developing a specific type of blood clot called deep venous thrombosis that most frequently occur in the legs. However, they are known to occur in other parts of the body such as the brain, eyes, liver as well as kidneys. This type of thrombophilia that is associated with Factor V Leiden is especially cruel as increases the chances that the clots will come loose from their original site and travel through the bloodstream from where they can get stuck in the lungs. This is also referred to as pulmonary embolism. This all sounds very horrifying, I know. However, not everyone with the mutation actually develops blood clots. Even though they are at a higher risk of developing clots, only 10% of those with the mutation go on to develop abnormal clots. Most probably the biggest issue with this mutation is among pregnant women (see below).

Genetics and Other Factors

Factor V Leiden thrombophilia is caused by a mutation in the F5 gene that is responsible for making a protein called coagulation factor V. Coagulation factor V is a protagonist in the coagulation system, which is the savior mechanism responsible for forming blood clots in response to injury. The mutation is recessive, which means that two copies are necessary for a person to actually suffer from Factor V Leiden thrombophilia.

In addition to genetics, lifestyle is a big issue when it comes to Factor V Leiden thrombophilia. Obesity, increasing age, injury, smoking, surgery, pregnancy as well as oral contraceptives and hormone replacement therapy are all factors that have all been associated with higher risks of this kind of thrombophilia.

Factor V Leiden and Pregnancy

Factor V Leiden and Pregnancy

The Factor V Leiden mutation is associated with the risk of miscarriage. In fact, pregnant women who have this mutation are about two to three times more likely to suffer multiple miscarriages or pregnancy loss during the second or third trimester. As if that is not bad enough, several studies have shown that there are several other risks associated with the mutation. These include pregnancy-induced high blood pressure (preeclampsia), early separation of the placenta from the uterus (placental abruption) as well as slow fetal growth or intrauterine growth restriction. However, it should be highlighted that these studies have to be replicated so that these findings can be confirmed.


So, to wrap things up, we need to answer the question, “Why is this test important?” The guidelines for testing considerations are straightforward. Those who have venous thrombosis under the age of 50, those who have recurrent venous thrombosis as well as family history of it, female smokers who suffered myocardial infarction under the age of 50, venous thrombosis in pregnant women or those taking oral contraceptives, women with recurrent pregnancy loss, unexplained severe preeclampsia, placental abruption as well as intrauterine fetal growth restriction are all individuals who can benefit from the test.

However, some research has implied that genetic testing for the mutation has been overused with little to no benefits. The claim is that finding out about having this mutation actually does not cause any change in people’s lifestyles. Furthermore, knowing that they have the mutation may only result in unnecessary worrying because so few people who actually carry the mutation develop the disease. This all holds true for those who are not at risk for thrombophilia as well as for those who are at a risk but either do not plan on becoming pregnant or are not pregnant.

However, given the problems it causes in pregnant women, the importance of the test becomes clear quickly. Surely, if a pregnant woman knew before her pregnancy that she is at a higher risk of thrombophilia because she has the mutation, she could take all the necessary precautions before getting pregnant in order to have a healthy pregnancy. There are medications that are given to those who have thicker blood so that they avoid possible pregnancy complications.

Laura Day