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What is Factor VII Assay?

Factor VII, also known as proconvertin or stable factor, is one of the proteins that help in the clotting of blood - the process by which our body stops excessive bleeding at the site of injury. It is produced in the liver with the help of vitamin K

Every time you get an injury, factor VII is activated along with a cascade of other proteins to initiate the clotting process systematically and stop bleeding.

However, people who have a deficiency of factor VII tend to have a faulty clotting process and hence suffer from prolonged bleeding. 

Factor VII test determines the level of factor VII in the blood to check for bleeding disorders. 

There are two types of factor VII deficiency:

  • Inherited deficiency/congenital deficiency: As the name suggests, this type of deficiency is inherited and is thus present since birth. People who have a congenital factor VII deficiency tend to have an absence or low levels of factor VII in their blood. However, it is a recessive genetic disorder - this means the child will only get this deficiency if both the parents are at least carriers of the faulty gene. Hence, inherited deficiency of factor VII is rare and affects about 1 in 300,000 to 500,000 individuals. 
  • Acquired deficiency: This type of deficiency is acquired at some point during a person’s life. It may be due to liver diseases, low levels of vitamin K or sepsis.
  1. Why is a Factor VII Assay performed?
  2. How do you prepare for a Factor VII test?
  3. How is a Factor VII test performed?
  4. What do Factor VII test results mean?

Your doctor may order this test if you tend to have prolonged bleeding - normal clotting time is between eight to 15 minutes. In a person with known factor VII deficiency, this test may be ordered to evaluate the severity of the deficiency or the effectiveness of the treatment. Symptoms of deficiency may differ based on the amount of factor VII present in the blood.

  • Mild deficiency of factor VII: This deficiency may or may not show any signs and symptoms. Prolonged bleeding may be experienced after trauma or surgery. Symptoms related to mild deficiency include:

  • Severe deficiency of factor VII: Severe deficiency of factor VII may mimic haemophilia and can be life-threatening due to spontaneous bleeding. Some of the symptoms of severe deficiency are: 
    • Bleeding in the stomach and intestine which may cause black and bloody stools 
    • Bleeding in the urinary tract which may result in blood in the urine 
    • Bleeding into the soft tissues that may result in deep bruises 
    • Bleeding into the joints which may damage the joints and affect joint movement
    • Bleeding in the brain (intracranial haemorrhage)

You do not require much preparation before this test. Inform your doctor about any prescribed or non-prescribed drugs and supplements that you may be taking, as some medications may affect the results of this test.

You will be given special instructions if you are on blood-thinning medications or anticoagulant therapy, e.g. you will be advised to avoid warfarin for two weeks or heparin therapy for two days before the test.

Your doctor or laboratory technician will draw a small blood sample from a vein in your arm using a sterile needle. The procedure usually takes less than three minutes. When the needle is inserted, you may experience mild pain. Other risks associated with a blood test include: 

  • Lightheadedness or fainting
  • Blood accumulation under the skin
  • Excessive bleeding
  • Multiple punctures to locate veins

In people with bleeding problems, the risk of excessive bleeding after the test is slightly greater than in healthy people. 

Normal results:

The normal level of factor VII ranges around 0.35-0.60 mg/L. This indicates that sufficient factor VII levels are present in your blood to promote normal clotting. 

Abnormal results:

Abnormal results indicate a low or high level of factor VII in the blood. A person may not experience abnormal bleeding even until they have less than 10% of the normal levels of the factor. However, bleeding episodes may be seen with levels less than 5%, and severe bleeding may occur when the level is less than 1%. There may be various underlying causes of abnormally low levels of factor VII. Some of the reasons are: 

Increased levels of factor VII levels in the blood can be caused by: 

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.

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References

  1. MedlinePlus Medical Encyclopedia: US National Library of Medicine; Factor V deficiency
  2. MedlinePlus Medical Encyclopedia: US National Library of Medicine; Factor VII deficiency
  3. Cleveland Clinic. [Internet]. Cleveland. Ohio. Bleeding disorders
  4. MedlinePlus Medical Encyclopedia: US National Library of Medicine; Factor VII assay
  5. National Organisation of Rare Disorders [Internet]. Danbury, CT, U.S. Factor VII Deficiency
  6. Andrew M et al (1987) Development of the Human Coagulation System in the Full-Term Infant, Blood 70:165-72. PMID: 3593964.
  7. Sevenet PO, Kaczor DA, Depasse F. Factor VII Deficiency: From Basics to Clinical Laboratory Diagnosis and Patient Management. Clin Appl Thromb Hemost. 2017 Oct; 23(7):703-710. PMID: 27701084.
  8. Chernecky CC, Berger BJ. Factor VII (stable factor, proconvertin, autoprothrombin I) - blood. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. St Louis, MO: Elsevier Saunders; 2013:503-504.
  9. Pai M. Laboratory evaluation of hemostatic and thrombotic disorders. In: Hoffman R, Benz EJ, Silberstein LE, et al, eds. Hematology: Basic Principles and Practice. 7th ed. Philadelphia, PA: Elsevier; 2018:chap 129.
  10. Randi J. Katz, Amir Steinberg and Robert Klafter. Factor VII Deficiency - A Restrospective Case Review. Blood 2006 108:4011