How is it used?
Fibrinogen is usually requested with other tests. It helps your doctor to evaluate your body's ability to form and break down blood clots. Fibrinogen may be used as a follow-up to an abnormal prothrombin time (PT) or activated partial prothrombin time (aPTT, or PTT) and/or an episode of prolonged or unexplained bleeding. It may be measured, along with tests such as PT, aPTT, platelets, fibrin degradation products (FDP), and D-dimer to help diagnose disseminated intravascular coagulation (DIC). 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 ).
Sometimes fibrinogen is requested with other cardiac risk markers such as high sensitivity C-reactive protein (hsCRP), to help determine a patient's overall risk of developing cardiovascular disease. This use of measuring fibrinogen levels has not gained widespread acceptance though, because there are no direct treatments for elevated levels. However, some doctors feel 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).
When is it requested?
The doctor may request a fibrinogen test when a patient has unexplained or prolonged bleeding and/or an abnormal PT and aPTT test result. The test can also be used when patients have of disseminated intravascular coagulation (), such as: bleeding gums, nausea, vomiting, severe muscle and abdominal pain, seizures and oliguria (decreased urine output), or when the doctor is monitoring treatment for DIC.
Fibrinogen testing can also be performed 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 over a period of time the clotting ability of a patient with an acquired bleeding disorder.
In some cases, fibrinogen testing is performed with other tests when the doctor wants to evaluate a patient's risk of developing cardiovascular disease.
What does the test result mean?
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 afibrinogenaemia (no production), or to an acquired condition such as liver disease or malnutrition that leads to hypofibrinogenaemia (low levels).
Acutely (that is, abruptly) low levels are often related to consumption of fibrinogen, such as may be seen with disseminated intravascular coagulation (DIC) and some cancers. These conditions use up large amounts of clotting factors, leading first to inappropriate clot formation then - as levels fall - to excessive bleeding. Reduced fibrinogen levels may also be seen, sometimes, following large volume blood transfusions (as stored blood loses fibrinogen). Fibrinolytic proteins that normally dissolve clots, may also reduce fibrinogen levels by both attacking fibrinogen and breaking down fibrin at an accelerated rate.
Normal fibrinogen levels usually reflect normal clotting, but may also be seen when a person has a sufficient quantity of fibrinogen, but the fibrinogen is not functioning normally – called dysfibrinogenaemia. 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. If clinical findings suggest a fibrinogen problem, other specialised tests may be done to evaluate fibrinogen function further.
Fibrinogen is an acute phase reactant, meaning that fibrinogen concentrations may rise sharply in any condition that causes or tissue damage. Elevated concentrations of fibrinogen are not specific - they do not tell the doctor the cause or location of the disturbance. Doctors often do not check for elevated fibrinogen levels in these situations because they expect them to be there. Usually these elevations are temporary; returning to normal after the underlying condition has been resolved.
Elevated levels may be seen with:
While fibrinogen levels are elevated, they may increase a person's risk of developing a blood clot and over time they could contribute to an increased risk for developing cardiovascular disease. This is why some doctors occasionally request fibrinogen with other cardiac risk markers.
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, fibrinolytic drugs (streptokinase, urokinase, tPA) and sodium valproate. Moderate elevations in fibrinogen may be seen sometimes with pregnancy, cigarette smoking, and with oral contraceptives, HRT or oestrogen use.
Dysfibrinogenaemia, 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. Dysfibrinogenaemia is associated predominantly with venous thrombosis (inappropriate blood clot formation in the veins). PT, aPTT, and thrombin time are used to screen for this condition which is then confirmed with additional specialised blood tests. Patients with fibrinogen deficiency or dysfibrinogenaemia may experience poor wound healing.