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Fibrinogen

Also known as: Factor I
Formal name: Fibrinogen
Related tests: Prothrombin Time (PT), Partial Thromboplastin Time (PTT), D-dimer, Coagulation Factors, Thrombin Time

The Test

How is it used?

Fibrinogen is usually ordered with other blood clotting tests. It helps your doctor to evaluate your body's ability to form a blood clot. Fibrinogen may be ordered as a follow-up to an abnormal Prothrombin Time (PT) or Partial Thromboplastin Time (PTT) and/or an episode of prolonged or unexplained bleeding. It may be measured, along with tests such as PT, PTT, platelets, fibrin degradation products (FDP), and D-dimer to help diagnose disseminated intravascular coagulation (DIC) or abnormal fibrinolysis. Occasionally, fibrinogen can be used 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 fibrinogen is ordered, along with other cardiac risk markers such as C-reactive protein (CRP), to help determine a patient's overall risk of developing cardiovascular disease. This use of fibrinogen has not gained widespread acceptance though, because there are no direct treatments for elevated levels. However, many doctors feel that fibrinogen measurements give them additional information that may lead them to be more aggressive in treating those risk factors that they can influence (such as cholesterol and HDL).

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When is it ordered?

The doctor may order a fibrinogen test when a patient has unexplained or prolonged bleeding or an abnormal PT and PTT test result. The test can also be ordered when patients have symptoms of or are undergoing treatment for DIC or abnormal fibrinolysis.

Fibrinogen testing can also be done along with other coagulation factor tests when there is suspicion that the patient may have an inherited factor deficiency or dysfunction, or when the doctor wants to evaluate and monitor the clotting ability (over time) of a patient with an acquired bleeding disorder.

In some cases, fibrinogen testing is performed along with other tests when the doctor wants to evaluate a patient's risk of developing cardiovascular disease.

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What does the test result mean?

Looking for reference ranges?

Fibrinogen levels are a reflection of clotting ability and activity in the body. Reduced concentrations of fibrinogen 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 DIC and abnormal fibrinolysis. Reduced fibrinogen levels may also occur following rapid, large-volume blood transfusions.

Normal fibrinogen levels usually reflect normal blood clotting ability. Rarely, a person may have a sufficient quantity of fibrinogen, but the fibrinogen does not function normally. This is usually due to a rare inherited abnormality in the gene that produces fibrinogen, which leads to the production of an abnormal fibrinogen protein (dysfibrinogenemia). If clinical findings suggest a fibrinogen problem, other specialized tests may be done to further evaluate fibrinogen function.

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 -- they do not tell the doctor the cause or location of the disturbance. Usually these elevations in the fibrinogen blood 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.

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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, androgens, Phenobarbital, streptokinase, urokinase, and valproic acid. Moderate elevations in fibrinogen may be seen sometimes with pregnancy, cigarette smoking, and with oral contraceptives or estrogen use.

Dysfibrinogenemia is a rare coagulation disorder caused by a mutation in the gene controlling the production of fibrinogen in the liver. It causes the liver to make an abnormal fibrinogen, one that resists degradation when converted to fibrin. Dysfibrinogenemia may increase a person's risk of venous thrombosis or rarely cause a mild bleeding tendency. PT, PTT, and Thrombin Time tests are used to screen for this condition, which is then confirmed with additional specialized blood tests. Patients with fibrinogen deficiency or dysfibrinogenemia may experience poor wound healing.

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