What is fibrinogen?

Fibrinogen (also known as factor I) is a glycoprotein in vertebrates that helps in the formation of blood clots. It consists of a linear array of three nodules held together by a very thin thread which is estimated to have a diameter between 8 and 15 Angstrom. It is a glycoprotein that is synthesized by the liver and plays and important role in the process of blood clotting. During normal blood coagulation in the human body, a coagulation cascade activates the zymogen prothrombin by converting it into the serine protease thrombin. Thrombin then converts the soluble fibrinogen into an insoluble fibrin strand. These strands are then cross-linked by factor XIII to form a blood clot where necessary in the body.

Congenital fibrinogen deficiency or disturbed function of fibrinogen can lead to either bleeding or thromboembolic complications, or is clinically without pathological findings. Acquired deficiency is found after hemodilution, blood losses and/or consumption such as in trauma patients, during some phases of the disseminated intravascular coagulation (DIC), and also in sepsis. In patients with fibrinogen deficiency, the correction of bleeding is possible by infusion of fresh frozen plasma (FFP), cryoprecipitate (a fibrinogen-rich plasma fraction) or by fibrinogen concentrates.


Why measure the level of fibrinogen?

Fibrinogen can be useful to reveal defects in clotting, there is often used when other coagulation tests (e.g. prothrombin time, thromboplastin time, activated partial thromboplastin time) that may give abnormal results. Fibrinogen levels can be measured in venous blood. In typical circumstances, fibrinogen is measured in citrated plasma samples in the laboratory, however the analysis of whole-blood samples by use of thromboelastometry (platelet function is inhibited with cytochalasin D) is also possible. Higher levels are, amongst others, associated with cardiovascular disease and may be elevated in any form of inflammation, as it is an acute-phase protein; for example, it is especially apparent in human gingival tissue during the initial phase of periodontal disease. Fibrinogen levels increase in pregnancy to an average of 4.5 g/l, compared to an average of 3 g/l in non-pregnant people.

The normal range of fibrinogen levels is around 200 to 400 mg/dL. However these values depend on the laboratory and the methods used. Abnormal results may be related to the body using up too much fibrinogen such as that in disseminated intravascular coagulation (DIC), or because of fibrinogen deficiency which may be acquired from birth or afterwards. Other causes may be due to the breakdown of fibrin (fibrinolysis), or that there is excessive bleeding (hemorrhage).


Standard of preparation

Sampling is usually done in the morning in the hospital. There are no special preparations needed for this test. The doctor will advise and recommend if you need to be fasting prior to the blood examination. You should inform your doctor of any medication you are taking prior to the exam, as some medical treatments may interfere with the blood results.


Is the examination painful or dangerous?

The examination is neither painful nor dangerous. The patient may feel a tingling sensation with the entrance of the needle in the arm when blood is being extracted for examination.


How is the exam performed?

The exam consists of a simple blood sample test.