Also Known As
Factor I
Fibrinogen Activity
Functional Fibrinogen
Fibrinogen Antigen
Plasma Fibrinogen
Hypofibrinogenemia Test
Formal Name
Fibrinogen Activity and Fibrinogen Antigen Assays
This article was last reviewed on
This article waslast modified on
May 22, 2018.
At a Glance
Why Get Tested?

As part of an investigation of a possible bleeding disorder or blood clot (thrombotic episode), particularly to evaluate the level and function of fibrinogen; sometimes used to help evaluate your risk of developing cardiovascular disease

When To Get Tested?

When you have bleeding or thrombotic episodes; when a PT and/or PTT test is prolonged; when you have a relative with a hereditary fibrinogen deficiency or abnormality; when your health care provider wants additional information to help evaluate your risk of developing heart disease

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

None

You may be able to find your test results on your laboratory's website or patient portal. However, you are currently at Lab Tests Online. You may have been directed here by your lab's website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab's website or portal, or contact your healthcare practitioner in order to obtain your test results.

Lab Tests Online is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.

The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.

If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.

Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called "normal" values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.

While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are "within normal limits."

For more information, please read the article Reference Ranges and What They Mean.

What is being tested?

Fibrinogen is a protein, a coagulation factor (factor I) that is essential for blood clot formation. Two types of tests are available to evaluate fibrinogen: a fibrinogen activity test evaluates how well fibrinogen functions in helping to form a blood clot while a fibrinogen antigen test measures the amount of fibrinogen in the blood.

Fibrinogen is produced by the liver and released into circulation along with several other coagulation factor proteins. Normally, when a body tissue or blood vessel wall is injured, a process called hemostasis begins to help stop the bleeding by forming a plug at the injury site. Small cell fragments called platelets adhere to and aggregate at the site, a coagulation cascade begins, and clotting factors are activated one after the other.

As the cascade nears completion, soluble fibrinogen is converted into insoluble fibrin threads. These threads crosslink together to form a fibrin net that stabilizes at the injury site. The fibrin net adheres to the site of injury along with the platelets to form a stable blood clot. This barrier prevents additional blood loss and remains in place until the injured area has healed.

For a stable clot to form there must be enough normally functioning platelets and coagulation factors. If there are dysfunctional factors or platelets, or too little or too much of them, it can lead to bleeding episodes and/or to formation of an in appropriate blood clot (thrombosis). Several laboratory tests, including fibrinogen tests, can be used to evaluate hemostasis.

It is now understood that coagulation tests are based on what happens artificially in the test setting (in vitro) and thus do not necessarily reflect what actually happens in the body (in vivo). Nevertheless, the tests can be used to evaluate specific components of the hemostasis system. The fibrinogen activity test evaluates that part of the hemostatic process in which soluble fibrinogen is converted into fibrin threads. With the addition of thrombin to the test sample, the fibrinogen test bypasses the rest of the coagulation factors and focuses on the function of fibrinogen.

  • A fibrinogen activity test measures the time that it takes for a fibrin clot to form following the addition of a standard amount of thrombin to plasma. This test evaluates the function of fibrinogen, its ability to be converted into fibrin. The time that is required for a clot to form directly correlates with the amount of active fibrinogen that is present. Prolonged clot-formation times may be due to decreased concentrations of normal fibrinogen or due to dysfunctional fibrinogen.
  • A fibrinogen antigen test uses a fibrinogen antibody to bind to fibrinogen in a blood sample. This test allows the quantity, but not activity, of fibrinogen to be measured.

Fibrinogen is also one of several blood factors that are called acute phase reactants. Blood levels of fibrinogen along with other acute phase reactants rise sharply with conditions causing acute tissue inflammation or damage. Tests for these acute phase reactants, including fibrinogen, may be performed to determine the extent of inflammation in the body.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into 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?

    This testing is used to evaluate fibrinogen, a protein that is essential for blood clot formation. When there is an injury and bleeding occurs, the body forms a blood clot through a series of steps. In one of the last steps, soluble fibrinogen is converted into insoluble fibrin threads that crosslink together to form a net that stabilizes and adheres at the injury site until the area has healed.

    Two types of tests are available:

    • A fibrinogen activity test measures the function of fibrinogen and its ability to be converted into fibrin. It is used:
    • A fibrinogen antigen test is occasionally ordered as a follow-up test to determine whether decreased fibrinogen activity is due to insufficient fibrinogen or dysfunctional fibrinogen (caused by inherited or acquired dysfibrinogenemia).
  • When is it ordered?

    A health practitioner may order a fibrinogen activity test when someone:

    • Has unexplained or prolonged bleeding
    • Has a thrombosis 
    • Has an abnormal PT and PTT test result
    • Has symptoms of or is undergoing treatment for DIC or abnormal fibrinolysis
    • May have an inherited or acquired coagulation factor (clotting protein) deficiency or dysfunction
    • Has an acquired bleeding disorder and the person's health practitioner wants to evaluate and monitor their clotting ability (over time)

    A fibrinogen antigen test may be performed when someone has a low result on a fibrinogen activity test to help determine whether it is due to insufficient or dysfunctional fibrinogen.

    High fibrinogen levels have also been associated with coronary heart disease, myocardial infarction, and peripheral arterial disease. In some cases, fibrinogen activity testing is performed along with other tests when a health practitioner wants to evaluate an individual's risk of developing cardiovascular disease.

  • What does the test result mean?

    Fibrinogen test results are reported as the concentration of the protein in the blood. Fibrinogen activity tests are converted into concentrations for comparison with fibrinogen antigen results.

    Normal fibrinogen activity results usually reflect normal blood clotting ability.

    Significantly decreased fibrinogen activity may be due to decreased or dysfunctional fibrinogen. Reduced fibrinogen activity and antigen levels may impair the body's ability to form a stable blood clot.

    Chronically low levels may be related to decreased production due to an inherited condition such as afibrinogenemia or hypofibrinogenemia or to an acquired condition such as end-stage liver disease or severe malnutrition.

    Acutely low levels are often related to consumption of fibrinogen such as may be seen with disseminated intravascular coagulation (DIC) and abnormal fibrinolysis, which occurs when the body is overactive in clearing blood clots. Reduced fibrinogen levels may also occur following rapid, large-volume blood transfusions and in people who are malnourished.

    Sometimes a health practitioner will use a ratio of the antigen test and the activity test. This is to help to distinguish dysfibrinogenemia (high ratio) from hypofibrinogenemia (ratio close to 1).

    Fibrinogen is an acute phase reactant, meaning that fibrinogen concentrations may rise sharply in any condition that causes inflammation or tissue damage. Elevated concentrations of fibrinogen are not specific; that is, they do not tell the health practitioner the cause or location of the disturbance. Usually these elevations in the fibrinogen level are temporary, returning to normal after the underlying condition has been resolved. Elevated levels may be seen with:

    While fibrinogen levels are elevated, a person's risk of developing a blood clot may be increased and, over time, they could contribute to an increased risk for developing cardiovascular disease.

  • Is there anything else I should know?

    Blood transfusions within the past month may affect fibrinogen test results.

    Certain drugs may cause decreased levels, including anabolic steroids, phenobarbital, streptokinase, urokinase, L-asparaginase, tissue plasmogen activators, and valproic acid. Moderate elevations in fibrinogen are sometimes seen with pregnancy, cigarette smoking, and with oral contraceptives or estrogen use.

    Dysfibrinogenemia is a rare coagulation disorder caused by mutations in the gene controlling the production of fibrinogen in the liver. It causes the liver to make an abnormal, dysfunctional fibrinogen, one that resists degradation when converted to fibrin or can not function normally in the coagulation cascade. Dysfibrinogenemia may increase a person's risk of venous thrombosis or, rarely, cause a mild bleeding tendency. People with fibrinogen deficiency or dysfibrinogenemia may experience poor wound healing.

    Genetic molecular testing is occasionally performed for those with inherited dysfibrinogenemia, hypofibrinogenemia, or afibrinogenemia to identify the genetic mutation responsible. Testing for this mutation may also be performed for other family members.

    People with liver disease may develop acquired dysfibrinogenemia that could contribute to bleeding or thrombosis.

  • What can I do to reduce my fibrinogen level?

    If your fibrinogen concentration is elevated due to pregnancy or to an acute inflammatory process, it will likely return to normal by itself once the underlying condition has resolved. If it is due to an acquired condition such as rheumatoid arthritis, there may be very little you can do to affect the level. If your health care provider has told you that elevated fibrinogen levels are increasing your risk of cardiovascular disease, you can make lifestyle changes that will affect other cardiac risk factors, such as reducing your cholesterol and raising your HDL. There is also some evidence that diets rich in omega-3 and omega-6 fatty acids (fish oils) may help reduce fibrinogen levels.

  • What is the difference between tests for fibrinogen, d-dimer, and fibrin degradation products (FDP)?

    Fibrinogen activity testing evaluates the conversion of fibrinogen into fibrin; fibrinogen antigen testing measures the amount of soluble Factor I (dissolved in the blood) before it has been turned into insoluble fibrin and been crosslinked into a fibrin net. D-dimer and FDP testing both help evaluate the status of the fibrinolytic system, the body's ability to break blood clots apart when they are no longer needed so that they can be removed. FDP is a measurement of all of the fragments of the dissolving clot, while D-dimer is a more specific measurement for one of the crosslinked, break-down fragments.

  • Can I have decreased or abnormal fibrinogen and not know it?

    Yes. Many people have relatively normal clotting even when fibrinogen concentrations and/or activity are low. Your condition may not be identified unless you bleed longer than expected after a surgical procedure or trauma or have coagulation-related testing performed for another reason, such as part of a pre-surgical screen.

View Sources

Sources Used in Current Review

Chen Y. (Updated 2013 March 3). Fibrinogen. MedlinePlus Medical Encyclopedia. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003650.htm through http://www.nlm.nih.gov. Accessed March 2013.

Wilczynski, C. et al. (Updated 2014 February 12). Fibrinogen. Medscape. http://emedicine.medscape.com/article/2085501-overview through http://emedicine.medscape.com. Accessed March 2013.

Balasa, V. (Updated 2012 May 16). Inherited Abnormalities of Fibrinogen Workup. Medscape. Available online at http://emedicine.medscape.com/article/960677-overview through http://emedicine.medscape.com. Accessed March 2013.

Burgess R. et. al. (Updated 2012 January 10). Dysfibrinogenemia. Medscape. Available online at http://emedicine.medscape.com/article/199723-overview through http://emedicine.medscape.com. Accessed March 2013.

Dugdale, D. and Chen, Y. (Updated 2011 February 21). Congenital afibrinogenemia. MedlinePlus Medical Encyclopedia. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/001313.htm through http://www.nlm.nih.gov. Accessed March 2013.

Pagana, K. D. & Pagana, T. J. (© 2013). Mosby's Diagnostic and Laboratory Test Reference 11th Edition: Mosby, Inc., Saint Louis, MO. Pp 445-446.

Sources Used in Previous Reviews

Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].

Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO. Pp 421-422

Coagulation Test Panels. Clinical and Research Laboratories, Florida Hospital Cancer Institute [On-line information]. Available online at http://www.fhci-labs.com/researchlabs/clinicallabs/hemostasisandthrombosis/panels.htm through http://www.fhci-labs.com.

Elstrom, R. (2001 November 25, Updated). Fibrinogen. MEDLINEplus Health Information, Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003650.htm.

Laposata, M. & Vancott, E. (2000 January). How to work up hypercoagulability. CAP In the News [On-line Coagulation Case Study]. Available online at http://www.cap.org/CAPToday/casestudy/coag5.html through http://www.cap.org.

Bleeding Disorders. The Merck Manual of Medical Information-Home Edition, Section 14. Blood Disorders, Chapter 155 [On-line information]. Available online at http://www.merck.com/mrkshared/mmanual_home/sec14/155.jsp through http://www.merck.com.

Venomous Bites and Stings. The Merck Manual of Medical Information-Home Edition, Section 24. Accidents and Injuries, Chapter 287 [On-line information]. Available online at http://www.merck.com/mrkshared/mmanual_home/sec24/287.jsp through http://www.merck.com.

Joist, (2000 April 19, Revised 4/19/00). What I Need to Know About Thrombophilia. Saint Louis University, Coagulation Consultants [On-line information]. Available online at http://www.slucare.edu/clinical/pathlab/coagulation/thrombophilia.shtml through http://www.slucare.edu.

Menta, S. (1999 Spring). The Coagulation Cascade. Physiology Disorders Evaluation, College of Medicine, Univ of Florida [On-line information]. Available online at http://www.medinfo.ufl.edu/year2/coag/title.html through http://www.medinfo.ufl.edu.

Elstrom, R. (2001 October 21, Updated). Bleeding disorders. MEDLINEplus Health Information, Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/001304.htm.

Elstrom, R. (2001 October 19, Updated). DIC (disseminated intravascular coagulation). MEDLINEplus Health Information, Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000573.htm.

Dugdale, D. (Updated 2009 March 2). Fibrinogen. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003650.htm. Accessed September 2010.

Balasa, V. (Updated 2010 July 28). Inherited Abnormalities of Fibrinogen. eMedicine. [On-line information]. Available online at http://emedicine.medscape.com/article/960677-overview through http://emedicine.medscape.com. Accessed September 2010.

Brick, W. et. al. (Updated 2009 November 17). Dysfibrinogenemia. eMedicine. [On-line information]. Available online at http://emedicine.medscape.com/article/199723-overview through http://emedicine.medscape.com. Accessed September 2010.

Dugdale, D. (Updated 2009 March 2). Congenital afibrinogenemia. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/001313.htm. Accessed September 2010.

Spence, R. et. al. (Updated 2010 January 12). Hemostatic Disorders, Nonplatelet eMedicine. [On-line information]. Available online at http://emedicine.medscape.com/article/210467-overview through http://emedicine.medscape.com. Accessed September 2010.

Pagana, K. D. & Pagana, T. J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 458-459.

Wu, A. (© 2006). Tietz Clinical Guide to Laboratory Tests, 4th Edition: Saunders Elsevier, St. Louis, MO. Pp 404-405.

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