The blood of the human body regulates protein and plasma. The molecules keep the blood healthy to run it smoothly through veins. Sometimes, harmful substances have developed the clotting tendencies. The protein that increases clotting into the blood acquires different dysfunctions. Antithrombin is a protein that kills the clotting enhancer molecules. If any person is addicted to the blood clot symptoms, then doctors prescribe the Antithrombin-III-Activity test. The physician collects a blood sample and sends to the laboratory to check the level of antithrombin protein. If the level decreases from the normal level, then the bodies are being attacked by the dangerous plasma items that clot the blood.