Antithrombin is a protein in the blood that helps regulate blood clotting. It works by inhibiting the activity of certain enzymes, particularly thrombin and factor Xa, which are crucial for the formation of blood clots. By controlling these enzymes, antithrombin plays a vital role in preventing excessive clotting, ensuring that blood flows smoothly throughout the body. A deficiency in antithrombin can lead to an increased risk of abnormal blood clots, a condition known as thrombosis. This can result in serious health issues, such as deep vein thrombosis or pulmonary embolism. Monitoring antithrombin levels is important for individuals with a history of clotting disorders.