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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]

The Test Sample

What is being tested?

Coagulation factor tests measure the function of proteins essential for blood clot formation. Each test evaluates one of several coagulation factors produced by the liver. When someone has an unexplained bleeding episode, one possible cause is a reduction in the level of a coagulation factor in their blood. Measuring these factors can help a doctor determine the cause of the bleeding and the best treatment. 

The adequacy of a coagulation factor is typically determined by measuring the activity of the factor in blood. Activity assays can detect reduced levels of protein or proteins that don't work properly (have reduced function). Rarely, the antigen level (quantity) 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 an injury occurs that results in bleeding, the coagulation system is activated and plugs the hole in the leaking blood vessel with a clot while still keeping blood flowing through the vessel by preventing the clot from getting too large. The coagulation system consists of a series of proteins (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 as the injury site is healed. 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.

  There are nine coagulation factor proteins that are routinely 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
I Fibrinogen
II Prothrombin
III Tissue factor
VIII Antihemophilic factor A

Antihemophilic factor B

(Christmas factor)

X Stuart-Prower factor
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.