Factor I (Fibrinogen) Deficiency

Factor I (also called fibrinogen) deficiency is an inherited bleeding disorder that is caused by a problem with factor I. As the body produces less fibrinogen than it should, or because the fibrinogen is not working properly, the clotting reaction is blocked prematurely and the blood clot does not form.

Factor I deficiency is an umbrella term for several related disorders known as congenital fibrinogen defects. Afibrinogenemia (a complete lack of fibrinogen) and hypofibrinogenemia (low levels of fibrinogen) are quantitative defects, meaning the amount of fibrinogen in the blood is abnormal. Dysfibrinogenemia is a qualitative defect in which fibrinogen does not work the way it should. Hypodysfibrinogenemia is a combined defect that involves both low levels of fibrinogen and impaired function.

Afibrinogenemia is an autosomal recessive disorder, which means that both parents must carry the defective gene in order to pass it on to their child. Like all autosomal recessive disorders, afibrinogenemia is found more frequently in areas of the world where marriage between close relatives is common. Hypofibrinogenemia, dysfibrinogenemia, and hypodysfibrinogenemia can be either recessive (both parents carry the gene) or dominant (only one parent carries and transmits the gene). All types of factor I deficiency affect both males and females.


The symptoms of factor I deficiency differ depending on which form of the disorder a person has.


  • Nosebleeds (epistaxis)
  • Easy bruising
  • Heavy or prolonged menstrual bleeding (menorrhagia)
  • Muscle bleeds
  • Bleeding into joints (hemarthrosis)
  • Bleeding from the umbilical cord stump at birth
  • Bleeding in the mouth, particularly after dental surgery or tooth extraction
  • Abnormal bleeding during or after injury, surgery, or childbirth
  • Abnormal bleeding after circumcision
  • Problems during pregnancy (including miscarriage)


Other reported symptoms

  • Bleeding in the gut (gastrointestinal haemorrhage)
  • Bleeding in the central nervous system (the brain and spinal cord)
  • Formation of blood clots (thrombosis)



Symptoms are similar to those seen in afibrinogenemia. As a general rule, the less factor I a person has in his/her blood, the more frequent and/or severe the symptoms.


Symptoms depend on how the fibrinogen (which is present in normal quantities) is functioning. Some people have no symptoms at all. Other people experience bleeding (similar to those seen in afibrinogenemia) and others show signs of thrombosis (abnormal blood clots in blood vessels) instead of bleeding.


Symptoms are variable and depend on the amount of fibrinogen that is produced and how it is functioning.


Factor I deficiency is diagnosed by a variety of blood tests, including a specific test that measures the amount of fibrinogen in the blood. However, low fibrinogen levels or abnormal function may be a sign of another disease, such as liver or kidney disorders, which should be ruled out before a bleeding disorder is diagnosed. Diagnostic tests should be performed by a specialist at a Comprehensive Care Centre.


There are three treatments available for factor I deficiency. All are made from human plasma.

  • Fibrinogen Concentrate
  • Cryoprecipitate
  • Fresh Frozen Plasma (FFP)


Treatment may also be given to prevent the formation of blood clots, as this complication can occur after fibrinogen replacement therapy.

Many people who have hypofibrinogenemia or dysfibrinogenemia do not need treatment. Excessive menstrual bleeding in women with factor I deficiency may be controlled with hormonal contraceptives (birth control pills) or antifibrinolytic drugs.

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