Clotting factors, or coagulation factors, are a series of proteins present in the blood and which play essential parts in the clotting process. There are 13 in all, and they are traditionally numbered using Roman numerals from I to XIII. When a blood vessel is cut, tiny blood particles called platelets collect at the injury site and chemicals are released which activate the clotting factors. Clotting then takes place in a sequence of complicated chemical reactions which ends with the creation of a protein known as fibrin. Fibrin forms a network of strands which combines with platelets and blood cells to create a clot.
There are important reasons for clotting, as without it cutting a blood vessel could lead to an individual bleeding to death. It is also vital that clotting does not occur inappropriately, as a clot blocking a healthy blood vessel can lead to a reduced blood supply to body tissue. This could have potentially serious consequences if that tissue is part of an essential organ such as the heart. In the blood, there are chemicals which break down clots, and normally there is an overall tendency toward dissolving clots. When a blood vessel becomes damaged, and blood loss is imminent, the system shifts toward creating clots.
A clotting deficiency can give rise to a bleeding disorder, where a cut is followed by an excessive loss of blood or where internal bleeding occurs. Deficiencies may arise when clotting factors are not produced in adequate amounts or when a specific clotting factor is faulty and fails to work. Causes of clotting problems include some liver diseases, as many coagulation factors are made in the liver. Not having enough vitamin K can also reduce coagulation factor levels, as the vitamin is necessary for the creation of some clotting factors.
Genetic disorders exist in which certain clotting factors are not made. Hemophilia A is a condition in which there is a lack of clotting factor VIII, and, in hemophilia B, there is a deficiency of factor IX. Other deficiencies are found much more rarely.
Hemophilias may be treated by giving the missing coagulation factors in the form of an infusion into a vein. In cases where hemophilia is severe, it may be necessary to administer clotting factors regularly, while in milder cases, infusions may only be required if bleeding occurs or in situations where it is anticipated, such as before surgery. With treatment, most individuals with hemophilia can expect a positive outlook.