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  • Also Known As:
  • Factor I Assay
  • Fibrinogen Activity (Functional)
  • Fibrinogen Antigen
  • Cardiac Fibrinogen
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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 (known as coagulation factor I); sometimes used to help evaluate your risk of developing cardiovascular disease

When To Get Tested?

When you have excessive bleeding (e.g., easy bruising, frequent nosebleeds, bleeding gums), a harmful blood clot, or both (e.g., DIC); when your prothrombin time (PT) and/or partial thromboplastin time (PTT) is prolonged; when you have a relative with a hereditary fibrinogen deficiency or abnormality; sometimes when your health care practitioner wants additional information to help evaluate your risk of heart disease

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?


You may be able to find your test results on your laboratory’s website or patient portal. However, you are currently at Testing.com. 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.

Testing.com 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, specifically a clotting factor (factor I), that is essential for proper 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. A fibrinogen antigen test measures the amount of fibrinogen in the blood.

Fibrinogen is produced by the liver and released into the blood along with several other clotting factors (also called coagulation factors). 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 cellular fragments called platelets clump and stick to the injury site and clotting factors are activated one after the other. This last part is called the coagulation cascade.

As the cascade nears completion, soluble fibrinogen is converted into insoluble fibrin threads. These threads then 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 is healed.

For a stable clot to form, there must be enough normally functioning platelets and coagulation factors. Too little, too much, or dysfunctional clotting factors or platelets can lead to bleeding episodes and/or to the formation of an inappropriate blood clot (thrombosis). Several laboratory tests, including fibrinogen tests, can be used to evaluate the clotting process. Fibrinogen testing includes:

  • A fibrinogen activity test evaluates that part of the clotting process in which soluble fibrinogen is converted into fibrin threads. It measures the time that it takes for a fibrin clot to form after a standard amount of thrombin is added to your blood sample (plasma). The time it takes 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 levels of normal fibrinogen or may be due to fibrinogen that does not function as it should (dysfunctional).
  • A fibrinogen antigen test measures the level of fibrinogen in a blood sample, including both functional and dysfunctional fibrinogen.

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.

Common Questions

How is it used?

This testing is used to evaluate fibrinogen (factor I), a protein that is essential for blood clot formation.

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:
    • As part of an investigation of a possible bleeding disorder or inappropriate blood clot formation (thrombotic episode)
    • As a follow-up to an abnormal bleeding disorder test (prothrombin time, PT or partial thromboplastin time, PTT) and/or an episode of prolonged or unexplained bleeding
    • Along with tests such as PT, PTT, platelet function tests, fibrin degradation products (FDP), and D-dimer to help diagnose disseminated intravascular coagulation (DIC) or abnormal fibrinolysis
    • Occasionally to help monitor the status of a progressive disease (such as liver disease) over time or, rarely, to monitor treatment of an acquired condition (such as DIC)
    • Sometimes along with other cardiac risk markers such as high-sensitivity C-reactive protein (hs-CRP) to help determine overall risk of cardiovascular disease. This use of the test has not gained widespread acceptance because there are no direct treatments for elevated levels. However, many healthcare practitioners feel that fibrinogen activity measurements give them additional information that may lead them to be more aggressive in treating those risk factors that they can treat (such as unhealthy levels of LDL cholesterol).
  • A fibrinogen antigen test is occasionally used as a follow-up test to determine whether decreased fibrinogen activity is due to insufficient fibrinogen or dysfunctional fibrinogen.

When is it ordered?

A healthcare practitioner may order a fibrinogen activity test when you have:

  • Unexplained or prolonged bleeding
  • A harmful blood clot (thrombosis)
  • Abnormal PT and PTT test results
  • Symptoms and signs of disseminated intravascular coagulation (DIC) or undergoing treatment for DIC or abnormal fibrinolysis
  • Symptoms suggesting an inherited or acquired coagulation factor (clotting protein) deficiency or dysfunction
  • Been diagnosed with an acquired bleeding disorder to evaluate and monitor your clotting ability (over time)

A fibrinogen antigen test may be performed when you have an abnormally low result on a fibrinogen activity test to help determine whether it is due to low fibrinogen or fibrinogen that does not function properly.

In some cases, fibrinogen testing may be performed along with other cardiac risk markers when your health care practitioner wants to have additional information to help evaluate your risk of heart 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. Results are usually interpreted in the context of results from other tests.

Normal fibrinogen activity results usually reflect normal contribution of fibrinogen to your blood clotting ability.

Significantly decreased fibrinogen activity may be due to a decreased amount of fibrinogen or fibrinogen that does not function as it should. Reduced fibrinogen activity and antigen levels may affect your ability to form a stable blood clot.

  • Low fibrinogen levels that persist over time (chronic) may be related to the body’s inability to produce fibrinogen due to:
    • An acquired condition such as end-stage liver disease or severe malnutrition
    • A rare inherited condition such as dysfibrinogenemia, afibrinogenemia or hypofibrinogenemia
  • Acutely low levels are often related to conditions in which fibrinogen is used up more quickly than the body can produce it. This can occur with disseminated intravascular coagulation (DIC) and abnormal fibrinolysis, which occurs when the body is overactive in breaking down and clearing blood clots.
  • Reduced fibrinogen levels may also occur following rapid, large-volume blood transfusions.

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

Fibrinogen is an acute phase reactant, meaning that fibrinogen levels may rise sharply in any condition that causes inflammation or tissue damage. High levels of fibrinogen are not specific. They do not tell the healthcare practitioner the cause or location of the inflammation or damage. Usually these increased levels are temporary, returning to normal after the underlying condition has resolved.

Increased fibrinogen levels may be seen with:

  • Infections
  • Cancer
  • Coronary heart disease, heart attack
  • Stroke
  • Inflammatory disorders (like rheumatoid arthritis and glomerulonephritis, a form of kidney disease)
  • Trauma
  • Peripheral artery disease
  • Heavy smoking

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 cardiovascular disease.

What are congenital (inherited) dysfibrinogenemia, hypofibrinogenemia and afibrinogenemia?

These are a rare inherited coagulation disorders caused by changes (mutations) in the genes controlling the production of fibrinogen in the liver.

  • Congenital dysfibrinogenemia causes the liver to make an abnormal, dysfunctional fibrinogen, one that resists degradation when converted to fibrin or cannot function normally in the coagulation cascade. Dysfibrinogenemia may increase a person’s risk of a blood clot or, rarely, cause a mild bleeding tendency. People with fibrinogen deficiency or dysfibrinogenemia may experience poor wound healing.
  • Congenital hypofibrinogenemia results in decreased fibrinogen. People with this condition can experience mild bleeding episodes, such as a bloody nose or bleeding gums.
  • Congenital afibrinogenemia is a severe lack of fibrinogen. People with this condition may be at risk of severe bleeding (hemorrhaging) episodes, especially as babies or as young children. They may experience excessive bleeding from the umbilical cord, frequent, easy bruising, nose bleeds that are difficult to stop, excessive bleeding after surgical procedures, and bleeding in the digestive tract.

Genetic testing is occasionally performed for people with these inherited disorders to identify the genetic mutation responsible. Testing for this mutation may also be performed for other family members.

If my fibrinogen level is increased, what can I do to reduce it?

If your fibrinogen concentration is elevated due to an acute inflammatory process, it will likely return to normal 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 LDL cholesterol and raising your HDL cholesterol. 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 fragments of the dissolving clot, while D-dimer is a more specific measurement for one of the final 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.

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 plasminogen activators (t-PA), and valproic acid. Moderate elevations in fibrinogen are sometimes seen with pregnancy, cigarette smoking, and with oral contraceptives or estrogen use.

View Sources

Sources Used in Current Review

Gersten, T. et. al. (2017 February 7, Updated). Fibrinogen blood test. MedlinePlus Medical Encyclopedia. Available online at https://medlineplus.gov/ency/article/003650.htm. Accessed February 2019.

Mir, M. (2016 May 12, Updated). Nonplatelet Hemostatic Disorders. Medscape Hematology. Available online at https://emedicine.medscape.com/article/210467-overview. Accessed February 2019.

Jackson, B. et. al. (2018 July, Updated). Uncommon Factor Deficiencies. ARUP Consult. Available online at https://arupconsult.com/content/factor-deficiencies-uncommon. Accessed February 2019.

(© 1995–2019). Fibrinogen, Plasma. Mayo Clinic Mayo Medical Laboratories. Available online at https://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/40937. Accessed February 2019.

Acharya, S. (2016 August 15, Updated). Inherited Abnormalities of Fibrinogen. Medscape Pediatrics: General Medicine. Available online at https://emedicine.medscape.com/article/960677-overview Accessed February 2019.

(2017 February 6, Reviewed). Hemophilia Diagnosis. Centers for Disease Control and Prevention. Available online at https://www.cdc.gov/ncbddd/hemophilia/diagnosis.html. Accessed February 2019.

Moake, J. and Cox, J.W. (2016 April, Updated). Overview of Hemostasis. Merck Manual Professional Version. Available online at https://www.merckmanuals.com/professional/hematology-and-oncology/hemostasis/overview-of-hemostasis. Accessed February 2019.

Wilczynski, C. (2014 February 12, Updated). Fibrinogen. Medscape Laboratory Medicine. Available online at https://emedicine.medscape.com/article/2085501-overview. Accessed February 2019.

(2018) National Organization for Rare Disorders. Congenital Afibrinogenemia. Available online at https://rarediseases.org/rare-diseases/afibrinogenemia-congenital/. Accessed February 2019.

(2016) National Organization for Rare Disorders. Dysfibrinogenemia. Available online at https://rarediseases.org/gard-rare-disease/2004/dysfibrinogenemia/. Accessed February 2019.

(7/14/2019) Genetic and Rare Diseases Information Center (GARD). Dysfibrinogenemia. Available online at https://rarediseases.info.nih.gov/diseases/2004/dysfibrinogenemia. Accessed February 2019.

(5/30/2016) Genetic and Rare Diseases Information Center (GARD). Afibrinogenemia. Available online at https://rarediseases.info.nih.gov/diseases/5761/afibrinogenemia. Accessed February 2019.

(10/15/2009) Genetic and Rare Diseases Information Center (GARD). Hypofibrinogenemia, familial. Available online at https://rarediseases.info.nih.gov/diseases/2887/hypofibrinogenemia-familial. Accessed February 2019.

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.

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.

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.

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.

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.

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.

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. 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. 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. 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.

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

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

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


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