Factor II /Prothrombin Mutation (G20210)

This test looks for a specific genetic variant in the prothrombin gene, known as Factor II c.20210G>A (also written G20210A). Prothrombin, or Factor II, is one of the proteins involved in blood clotting. This variant causes the body to produce slightly more prothrombin than usual, which raises the tendency of the blood to form clots. It is one of the most common inherited causes of an increased clotting risk. This test uses a reliable method (PCR-RFLP) to detect whether the variant is present.

What it can help assess

• Inherited clotting risk (thrombophilia): identifying whether you carry this variant, which is associated with an increased tendency to form abnormal blood clots
• Understanding personal or family history: particularly relevant if you or a close relative have had a blood clot, such as a deep vein thrombosis (DVT) or pulmonary embolism (PE), or if there is a known family history of this variant
• Informing decisions in higher-risk situations: such as pregnancy, use of hormonal contraception or hormone therapy, surgery, or periods of immobility, where clotting risk is already increased

Understanding the results

You inherit two copies of the prothrombin gene, one from each parent. This test can identify:

• No variant detected: you do not carry the c.20210G>A variant
• One copy (heterozygous): you carry one copy, associated with a modestly increased clotting risk
• Two copies (homozygous): you carry two copies, associated with a higher clotting risk. This is less common

An important note on interpretation

Carrying this variant indicates an increased tendency to clot, not a certainty that a clot will occur. Many people who carry it never have a clot, and other factors, including lifestyle, medication, and other medical conditions, also play an important role. Results are best interpreted alongside your personal and family history, and any positive or significant result should be discussed with your GP or a specialist, who may recommend genetic counselling.

Why it matters

Understanding your inherited clotting risk can help you and your doctor make informed decisions, particularly around situations that carry a higher risk of clots. It can be especially valuable if you have a personal or family history of blood clots, or a known family history of this variant.

• Prothrombin (Factor II) gene, c.20210G>A variant (by PCR-RFLP)

No special preparation required.

For blood tests, we recommend drinking plenty of water beforehand to ensure smooth sample collection. If you are taking any regular medication, continue to do so unless advised otherwise by your doctor.