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:
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 C-reactive protein (CRP) to help determine a person's overall risk of developing cardiovascular disease. This use of the test has not gained widespread acceptance though because there are no direct treatments for elevated levels. However, many health 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 cholesterol).
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).
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.
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:
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.
This article was last reviewed on April 10, 2014. | This article was last modified on April 10, 2014.
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