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
Factor number or name
This article was last reviewed on
This article waslast modified on 29 January 2019.
At a Glance
Why Get Tested?

To determine whether one or more of your coagulation factors are decreased, absent or increased.

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; you may be tested when your doctor wants to monitor the severity of a factor deficiency and/or the effectiveness of treatment

Sample Required?

A blood sample taken from a vein in your arm

Test Preparation Needed?


On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you may be able to access your results online. Your GP practice will be able to provide specific details.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, sex, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

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.

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

No test preparation is needed.

Accordion Title
Common Questions
  • How is it used?

    Coagulation factor levels are used by health care professionals to determine if the factor is low or absent, associated with reduced clot formation and bleeding, or too high, sometimes associated with too much clot formation and thrombosis. Coagulation factor levels may also be measured to monitor the level during therapy.

  • When is it requested?

    Coagulation factor tests may be requested when someone is experiencing excessive bleeding or bruising or has a prolonged Prothrombin Time (PT) or Activated Partial Thromboplastin Time (aPTT). These tests are used as screening tools to determine whether one has a coagulation problem.

    Factor testing may be done if an inherited factor deficiency is suspected, especially when bleeding episodes begin early in life or when a close relative has an inherited factor deficiency. If an inherited deficiency is suspected, other family members may also be tested to help confirm the patient’s diagnosis and to establish whether they may be carriers of the condition or have the deficiency themselves (in an asymptomatic or less severe form).

    Coagulation factors may be measured when the patient is suspected of having an acquired condition that is causing bleeding, such as vitamin K deficiency or liver disease.

    Sometimes factor testing may be done on a patient with a known deficiency to monitor the factor deficiency and to evaluate the effectiveness of treatment.

  • What does the test result mean?

    Normal coagulation factor activity usually means normal clotting function. Low activity of one or more coagulation factors usually means impaired clotting ability. Each coagulation factor must be present in sufficient quantity in order for normal clotting to occur, but the level required is different for each factor. Results are frequently reported as a percentage with 100% being normal. For example, a factor VIII that is 30% would be considered abnormally low.

    Deficiencies in coagulation factors may be acquired (due to other diseases) or inherited, mild or severe, permanent or temporary. Those that are inherited are rare and tend to involve only one factor, which may be reduced or absent. Haemophilia A and B are the most common examples of inherited disorders. They are X-linked deficiencies of factors VIII and IX that occur almost exclusively in men (women are usually carriers who are asymptomatic or have mild bleeding). 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 the factor involved and amount available. Symptoms may vary from episode to episode, from excessive bleeding after dental procedures to severe recurrent bleeding into joints or muscles. Patients with a modest reduction in coagulation factor level may experience few symptoms and may discover their deficiency as an adult - after a surgical procedure or trauma or during screening that includes a Prothrombin Time (PT) or Activated Partial Thromboplastin Time (aPTT) test. Those with severe factor deficiencies may have their first bleeding episode very early; for example, a male infant with a deficiency of Factor VIII, IX, or XIII may bleed excessively after circumcision.

    Acquired deficiencies may be due to chronic diseases, 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 or treatment with a vitamin K antagonist like warfarin (the production of factors II, VII, IX, and X require vitamin K). If more than one clotting factor is decreased, it is usually due to an acquired condition. Factors may be decreased because of:  

    • consumption due to extensive clotting
    • liver disease
    • some cancers
    • severe infections
    • exposure to snake venom
    • vitamin K deficiency
    • anticoagulation therapy
    • accidental ingestion of the anticoagulant warfarin or some poisons
    • multiple blood transfusions (stored units of blood lose some of their clotting factors)

    Elevated levels of several factors are seen in situations of acute illness, stress, or inflammation. Some patients have persistent elevations of factor VIII that may be associated with an increased risk of venous thrombosis.

  • Is there anything else I should know?

    For both inherited and acquired factor deficiencies, the missing factor(s), once identified, can be replaced as needed. This may be done with a transfusion of fresh frozen plasma (FFP), which contains all of the missing factors, with a concentrated cryoprecipitate, with replacement factors (available commercially either recombinant factor predominantly used in children or plasma derived factors), or with desmopressin (DDAVP) - a drug that stimulates the body to release more factor VIII. These treatments may be used during a bleeding episode or to prevent excessive bleeding during an upcoming surgery or dental procedure.

  • What is von Willebrand factor?

    von Willebrand factor is responsible for helping platelets stick to the injured blood vessel wall. A blood clot then occurs around platelets at the site of injury. A deficiency or abnormality in von Willebrand factor can cause von Willebrand disease, an inherited bleeding disorder. It is associated with a secondary decrease in factor VIII concentration, as von Willebrand factor also binds to and stabilizes factor VIII in the blood stream. While von Willebrand factor may be used with coagulation factors if an inherited factor deficiency is suspected, it is usually considered separately because it is associated with platelets and not part of the classic coagulation cascade.

  • Why are some inherited bleeding disorders more severe than others?

    The severity of bleeding depends on the individual, the degree of abnormal factor concentration and/or function as well as which factor is deficient. Those who have a missing factor or one with very low activity will have more severe manifestations of the disease. Patients with one normal gene copy and one altered gene copy (heterozygous) will tend to have less severe bleeding than those with two altered copies (homozygous). Patients with a deficiency of factor XII are usually asymptomatic. This rare factor deficiency causes abnormal aPTT results but is not associated with increased bleeding. It may even be associated with a mild tendency to form clots.