At a glance
Also known as
Blood clotting factors have been named using roman numerals. Some of them have more common names, for example, factor I is also known as fibrinogen, factor II is known as prothrombin.
Why get tested?
To determine whether one or more of your coagulation factors is missing, deficient or not functioning properly.
When to get tested?
When you have unexplained or prolonged bleeding and /or easy bruising, an abnormal prothrombin time (PT) or activated partial thromboplastin time (APTT) test, or have a relative with a known hereditary coagulation factor deficiency. If you have been treated for a factor deficiency, a blood test can help determine the success of that treatment.
A blood sample is normally drawn from a vein in your arm.
Test preparation needed?
None needed for factor tests. If you are being tested for blood platelet function, your doctor may ask you to refrain from taking certain drugs one week prior to the test, for example, aspirin or ibuprofen (Neurofen).
What is being tested?
Coagulation factors are proteins that are essential for blood clot formation. Produced by the liver or blood vessels, the coagulation factors are continuously released into the bloodstream. When an injury occurs these factors are activated in a step by step process called the coagulation cascade. This cascade has two branches: when damage occurs to tissue, the body responds by activating the extrinsic pathway followed by the intrinsic pathway. 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 which form a mesh-like structure. The fibrin mesh along with aggregated cell fragments called platelets, forms a stable blood clot. Blood clots are red in colour because red cells are caught in the mesh. 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.
TYPES OF FACTOR DEFICIENCIES
About 12 of the 20 different factors involved in the coagulation cascade are vital to normal blood clotting. These 12 have individual names but are often referred to by their number, for instance factor VIII (factor 8; fVIII). 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 partly or completly deficient or not functioning correctly. Haemophilia A and B are the most common examples of inherited disorders. Haemophilia A is a defect or deficiency of factor VIII and Haemophilia B is a defect or deficiency of factor IX. 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 ). Other inherited factor deficiencies are not associated with the X chromosome and are much rarer than Haemophilia A and B.
The severity of 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 , 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 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.