To determine whether levels of one or more of your coagulation factors are increased, normal, or decreased
When you have unexplained or prolonged bleeding, abnormal results on coagulation screening tests such as prothrombin time (PT) or partial thromboplastin time (PTT), or have a relative with a hereditary coagulation factor deficiency; you may be tested when your healthcare practitioner wants to monitor the severity of a factor deficiency and/or the effectiveness of treatment.
A blood sample drawn from a vein in your arm
Coagulation factors are proteins circulating in the blood that are essential for proper blood clot formation. Coagulation factor tests measure the function of or sometimes the amount of these proteins in the blood.
Blood clotting is a complex process that involves numerous coagulation factors, which are produced by the liver and blood vessels. Each coagulation factor is evaluated with one or more tests. When factor levels are low, it can cause blood clotting to fail, leading to unexplained bleeding episodes. Measuring coagulation factors can help a healthcare practitioner determine the cause of the bleeding and the best treatment.
Coagulation factors are usually tested by measuring the factor's activity level in the blood. Activity assays can detect reduced levels of protein or proteins that don't function properly. Rarely, the amount (antigen level) of a coagulation factor may also be measured. Coagulation factor antigen tests can tell how much of the protein is present, but not whether its function is normal.
When someone bleeds (e.g., with an injury), the coagulation system is activated, plugging the leaking blood vessel with a clot. The coagulation system consists of a series of coagulation factors that activate in a step-by-step process called the coagulation cascade. The end result is the formation of insoluble fibrin threads that link together at the site of injury, along with aggregated cell fragments called platelets, to form a stable blood clot. The clot prevents additional blood loss and remains in place until the injured area has healed.
Blood clotting is dynamic; once a clot is formed, other factors are activated that slow clotting or dissolve the clot in a process called fibrinolysis. The clot is eventually removed after the injury site heals. In normal healthy individuals, this balance between clot formation and removal ensures that bleeding does not become excessive and that clots are removed once they are no longer needed.
For people with bleeding disorders, clotting does not work properly because they lack platelets or coagulation factors, or their platelets or factors don't work properly. There are a variety of bleeding disorders that may be passed through families (inherited) or acquired after birth. If a person has signs and symptoms of one of these disorders, coagulation factor testing may be ordered to help determine the diagnosis and treatment.
There are nine coagulation factor proteins that can be measured clinically (see table below). These factors are referred to by a name or Roman numeral or both in some cases. For example, coagulation factor II is also known as prothrombin. When one or more of these factors are produced in too small a quantity, or are not functioning correctly, they can cause excessive bleeding.
|coagulation factor||other common name|
|V||Proaccelerin or labile factor|
|VIII||Antihemophilic factor A|
Antihemophilic factor B
|XI||Plasma thromboplastin antecendent|
|XIII||Fibrin stabilizing factor|
How is it used?
Coagulation factor testing is performed to determine if a person has enough coagulation activity to control the blood clotting process. It is used by healthcare practitioners to determine if the level of a coagulation factor is low or absent (below the detectable limit) or if it is too high. Low coagulation factor activity is associated with reduced clot formation and excess bleeding. High coagulation factor activity can be associated with too much clot formation (thrombosis) and blockade in the circulatory system (thromboembolism).
One or more coagulation factor activity tests may be ordered to evaluate the function of specific factors. If a test result shows reduced activity, then an antigen test may be ordered as a follow-up test. This is occasionally done to determine if the low activity is due to a decreased quantity of a normal coagulation factor or due to a coagulation factor that does not function normally.
Coagulation factor testing may sometimes be ordered if a person has a family history of bleeding.
When is it ordered?
Coagulation factor tests are typically ordered when someone has a prolonged prothrombin time (PT) and/or partial thromboplastin time (PTT). The PT and PTT tests are used as screening tools to determine if someone has a coagulation problem or as part of an investigative workup when someone has signs and symptoms of a bleeding disorder, such as unexplained bruising, bleeding gums, excess bleeding from small cuts, or frequent nose bleeds.
Factor testing may be done when a healthcare practitioner suspects that a patient has an inherited coagulation factor deficiency such as Von Willebrand disease or hemophilia A, especially when bleeding episodes begin early in life or when a close relative has an inherited factor deficiency. When an inherited deficiency is suspected, other family members may also be tested to help confirm the person's diagnosis and to establish whether they may be carriers of the condition or have the deficiency themselves (in an asymptomatic or less severe form).
Sometimes factor testing may be done for a person with a known deficiency to monitor the factor deficiency and to evaluate the effectiveness of treatment.
Occasionally, factor testing is ordered when someone has an unexplained blood clot (thrombosis) to determine whether abnormally high factor activity is the underlying cause (e.g., elevated factor VIII activity is associated with excess clotting).
What does the test result mean?
Normal coagulation factor activity usually means normal clotting function. Low activity of one or more coagulation factors usually means impaired clotting ability. Each coagulation factor must be present in sufficient quantity in order for normal clotting to occur, but the level required is different for each factor. Results are frequently reported as a percentage with 100% being normal. For example, a factor VIII that is 30% would be considered abnormally low.
Deficiencies in coagulation factors can develop in several different ways. They may be acquired as part of other diseases or inherited. Deficiencies vary in severity and may be permanent or temporary.
- Excess blood clotting that uses up coagulation factor (e.g., disseminated intravascular coagulation)
- Liver disease (i.e., cirrhosis)
- Some cancers
- Exposure to snake venom
- Fat malabsorption
- Vitamin K deficiency
- Anticoagulation therapy (warfarin)
- Massive blood transfusions (e.g., transfuse only red blood cell units)
Inherited coagulation factor deficiencies are rare. They tend to involve only one factor, which may be reduced or absent (below the detectable limit).
Hemophilia A and B are the most common examples of inherited disorders. They are X-linked deficiencies of factors VIII and IX that occur almost exclusively in men. Women are more likely to be asymptomatic carriers of these genetic traits or have mild bleeding. Other inherited factor deficiencies, not associated with the X chromosome, are found equally in both men and women.
The severity of symptoms associated with an inherited factor deficiency depends on the factor involved, its functionality, and the amount of factor available. Symptoms may vary from episode to episode, ranging from excessive bleeding after dental procedures to severe recurrent bleeding into joints or muscles.
Individuals with a modest reduction in coagulation factor activity may have few symptoms and may discover their deficiency in adulthood, after a surgical procedure or trauma or during screening that includes a prothrombin time (PT) or partial thromboplastin time (PTT) test.
Individuals with severe factor deficiencies may have their first bleeding episode very early; for example, a male infant with a deficiency of Factor VIII, IX, or XIII may bleed excessively after circumcision.
Elevated levels of several factors are seen in situations of acute illness, stress, or inflammation. Some people have persistent elevations of factor VIII that may be associated with an increased risk of venous thrombosis.
Is there anything else I should know?
For both inherited and acquired factor deficiencies, the missing factor(s), once identified, can be replaced as needed. This may be done with a transfusion of fresh frozen plasma (FFP), which contains various coagulation factors, with a concentrated cryoprecipitate, or with replacement factors (some are available commercially, such as recombinant factor VIII). These treatments may be used during a bleeding episode or as a preventive measure to prevent excessive bleeding during an upcoming surgery or other invasive procedure.
What is von Willebrand factor?
The von Willebrand factor (vWF) is responsible for helping platelets stick to the injured blood vessel wall. It is also the carrier protein for factor VIII. A deficiency in von Willebrand factor can cause von Willebrand disease, an inherited bleeding disorder. While von Willebrand factor may be ordered along with coagulation factors if an inherited factor deficiency is suspected, it is usually considered separately because it is mainly associated with platelets and not part of the classic coagulation cascade.
Why are some inherited bleeding disorders more severe than others?
The severity of bleeding depends on the individual, the degree of abnormality of the factor involved, as well as which factor is deficient. Those who have a severely deficient factor or one with significant factor dysfunction will have more severe manifestations of the disease. People with one normal gene copy and one altered gene copy (heterozygous) will tend to have less severe bleeding than those with two altered copies (homozygous).
It should be pointed out that people with a deficiency of factor XII are usually asymptomatic. This rare factor deficiency causes abnormal PTT results but is not associated with increased bleeding risk.