Fibrinogen (Factor I)


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Subject: Fibrinogen (Factor I)

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  • Fibrinogen is a glycoprotein synthesized in the liver. It is modified by thrombin to become fibrin, a visible clot. It is also an acute-phase reactant.

  • Normal range: 150–400 mg/dL (most abundant circulating clotting factor).


  • This test detects decreased or abnormal fibrinogen.

  • It may be used to determine the severity and evolution of DIC by performing serial determinations.

  • Because of the initial elevation of fibrinogen, its determination is not useful in the diagnosis of DIC.


  • Severe fibrinogen deficiency may prolong PT, PTT, and TT.

Increased In

  • Acute inflammatory/infectious processes

  • Cancer

  • Pregnancy and use of oral contraceptives

  • Older age

  • Early DIC

Decreased In

  • Congenital afibrinogenemia or hypofibrinogenemia.

  • Dysfibrinogenemia (congenital or acquired).

  • DIC and pathologic fibrinolysis. Fibrinogen is consumed after initial elevation as an acute-phase reactant.

  • Very advanced liver disease.



  • Clotted specimens or those obtained with the wrong anticoagulant

  • Inappropriately filled test tubes

  • Inappropriately stored blood

  • Hyperlipidemic, icteric, or hemolyzed blood

  • Hct >55%