Fibrinogen

Normal range 2.0-4.0g/L. Produced by liver, it is an acute phase protein, raised in inflammatory reactions, pregnancy, stress, etc. Converted into fibrin by the action of thrombin and is a key component of a clot. Abnormalities of fibrinogen are more often acquired than inherited. Inherited defects are usually quantitative and include heterozygous hypofibrinogenaemia or homozygous afibrinogenaemia. Qualitative defects—the dysfibrinogenaemias—are inherited as incomplete autosomal dominant traits with >200 reported fibrinogen variants; defective fibrin polymerisation or fibrinopeptide release may occur. Most patients are heterozygous.

Clinical presentation

Symptoms of bruising, bleeding usually after trauma or operations will depend on the concentration and are more severe when <0.5g/L. Afibrinogenaemia (fibrinogen <0.2g/L) is a severe disorder with spontaneous bleeding, cerebral and gastrointestinal haemorrhage and haemarthrosis. It may present as haemorrhage in the newborn. Recurrent miscarriages occur. Most patients with dysfibrinogenaemia are heterozygous and bleeding symptoms are usually minor; arterial and venous thrombosis is described with some variants.

Diagnosis

4 PT, APTT and thrombin time; in afibrinogenaemia, the blood may be unclottable. Fibrinogen level measured by Clauss assay. Acquired hypofibrinogenaemia needs to be excluded (DlC, liver disease) and family studies are necessary.

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