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 factors are a group of proteins essential for blood clot formation. When a patient has an unexplained bleeding episode, one possible cause is a reduction in the level of a coagulation factor in their blood. Measuring the level of these factors can help a doctor determine the cause of the bleeding and the best treatment. Levels may also be measured if someone has a family history of bleeding.

In most cases, the level of a coagulation factor is determined by measuring the activity or function 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 of a coagulation factor may 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 bleeding 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 and begin to dissolve the clot in a process called fibrinolysis. The clot is eventually removed as the injured site is healed. In normal healthy individuals, this balance between clot formation and removal ensures that bleeding does not become excessive, and that clots only occur where and for as long as they are 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 missing, produced in too small a quantity, or not functioning correctly, they can cause excessive bleeding.



Other Common Name






Proaccelerin, labile factor




Antihaemophilic factor A


Antihaemophilic factor B


Thrombokinase, Stuart-Prower factor


Antihaemophilic factor C


Hageman factor


Fibrin stabilising factor

How is the sample collected for testing?

A blood sample is collected 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.