Coagulant, koh AG yuh luhnt, is any substance that causes a fluid to clot, or thicken. Milk curdles because rennin, an enzyme, causes clots to form. One of the most important coagulant actions is the clotting of blood. Scientists have found many blood-clotting factors. The combined action of all of these factors produces a blood clot. If any one clotting factor is missing, the tendency for blood to clot is reduced. Doctors then try to supply the missing substance. For example, in the blood disease hemophilia, doctors use an antihemophilic globulin to help the blood to clot. In other diseases, they may give the patient vitamin K or fibrinogen to induce the blood to clot and control hemorrhages.