Hypercoagulable states fall into two groups:
Inherited means you are born with the tendency to form abnormal blood clots. Common inherited conditions that affect clotting are factor V Leiden and the prothrombin mutation 20210A. Rare inherited conditions include protein C, protein S, and antithrombin III deficiencies.
Acquired means you develop the tendency to form abnormal blood clots later in life. Some medical situations can lead to the formation of abnormal blood clots. These include cancer, recent surgery or trauma, obesity, liver or kidney disease, and use of certain medications.
Situations that can lead to the formation of blood clots include prolonged bedrest, dehydration, poor positioning (such as crossing the legs), sitting for long periods (such as in a plane or car), and long-term use of an intravenous catheter.
Women who take birth control pills or hormone replacement therapy are more likely to develop blood clots. This risk is greatly increased in those who also smoke. The time before, during, and after pregnancy also increases the risk of clots.