Coagulation factors

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Also known as: Blood clotting factors; clotting factors [by individual factor number (Factor I, Factor II, etc.) or name (fibrinogen, prothrombin, etc.)]
Formal name: see table

At a Glance

Why Get Tested?

To determine whether one or more of your coagulation factors is missing, deficient or dysfunctional.

When to Get Tested?

When you have unexplained or prolonged bleeding, an abnormal prothrombin time (PT) or activated partial thromboplastin time (aPTT) test, or have a relative with a hereditary coagulation factor deficiency. Sometimes when your doctor wants to monitor the severity of a factor deficiency and the effectiveness of treatment.

Sample Required?

A blood sample drawn from a vein in your arm, or sometimes, via fingerstick

Test Preparation Needed?

None

The Test Sample

What is being tested?

Coagulation factors are proteins that are essential for blood clot formation. Produced by the liver, the coagulation factors are released into the bloodstream when an injury occurs and are activated in a step by step process called the coagulation cascade. This cascade has two branches: if the damage is to tissue the body responds by activating the extrinsic pathway. If the injury is to a blood vessel wall, the intrinsic pathway is activated. Each of these pathways utilises different coagulation factors but both come together to complete the clotting process in the common pathway.

Normally, by the end of the common pathway soluble fibrinogen (factor I) has been changed into insoluble fibrin threads. These threads have been crosslinked to make a fibrin net and stabilised at the injury site. They adhere there, along with aggregated cell fragments called platelets, to form a stable blood clot. This barrier prevents additional blood loss and remains in place until the area has healed. When the clot is no longer needed other factors are activated to dissolve and remove it.

About 12 of the 20 different factors involved in the coagulation cascade are vital to normal blood clotting. These 12 have individual names (see table) but are often referred to by their number, for instance Factor VIII (factor 8). When one or more of these factors are missing, produced in too small a quantity, or are not functioning correctly they can cause excessive bleeding and lead to bleeding disorders.

Deficiencies in coagulation factors may be acquired or inherited, mild or severe, permanent or temporary. Those that are inherited are rare and tend to involve only one factor, which may be absent, deficient or dysfunctional. Haemophilia A and B are the most common examples of inherited disorders. They are X-linked deficiencies (located on an X chromosome) of Factors VIII and IX that occur almost exclusively in men (women are usually asymptomatic carriers). Other inherited factor deficiencies, not associated with the X chromosome, are found equally in both men and women.

The severity of symptoms experienced by a patient with an inherited factor deficiency depends on which factor is involved, how much of it is available and whether or not it is functioning normally. Symptoms may vary from episode to episode, from a minor prolonged nosebleed to severe recurrent bleeding into areas such as the joints. While a patient may not have trouble with a small puncture or cut, a surgery, dental procedure, or trauma could put them into a bleeding crisis. Those with severe factor deficiencies may have their first bleeding episode very early, for example a male infant with a Factor VIII deficiency may bleed excessively after circumcision. On the other hand, patients with mild bleeding disorders may experience few symptoms and may discover their deficiency as an adult - after a surgical procedure or trauma, or during a screening that includes a PT or aPTT test.

Acquired deficiencies may be due to chronic disease, such as liver disease or cancer; to an acute condition such as disseminated intravascular coagulation (DIC), which uses up clotting factors at a rapid rate); or to a deficiency in vitamin K (the production of factors II, VII, IX, and X requires vitamin K). They may also be due to anticoagulant medications such as heparin or warfarin. Acquired conditions may involve multiple factor deficiencies that must be identified and addressed.

How is the sample collected for testing?

Typically, a blood sample is drawn from a vein in the arm. As an alternative, particularly in paediatric care, the blood sample is drawn from the fingertip.

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

No test preparation is needed.

The Test

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.