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Coagulation Factors

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Also known as: Factor Assays; Blood Clotting Factors; Clotting Factors [or by the individual factor number (Factor I, Factor II, etc.) or name (Fibrinogen, Prothrombin, etc.)]
Formal name: [see table]

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The Test Sample

What is being tested?

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 factorother common name
I Fibrinogen
II Prothrombin
V Proaccelerin or labile factor
VII Proconvertin
VIII Antihemophilic factor A

Antihemophilic factor B

(Christmas factor)

X Stuart-Prower factor
XI Plasma thromboplastin antecendent
XIII Fibrin stabilizing factor

How is the sample collected for testing?

A blood sample is drawn from a vein in the arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.