Appropriate levels of fibrinogen are necessary to maintain hemostasis and to cause platelets to aggregate. The reference range for fibrinogen is 200 to 400 mg/dL. Fibrinogen is an acute-phase reactant, meaning that there will be a transient increase in fibrinogen during inflammation, pregnancy, stress, and diabetes and when taking oral contraceptives. Therefore, a careful patient history is necessary when evaluating a problem involving fibrinogen. For the most part, decreases in fibrino-gen result from acquired disorders such as acute liver disease, acute renal disease, or disseminated intravascular coagulation. Acquired increases in fibrinogen may be demonstrated in hepatitis patients, pregnant patients, or those with atherosclerosis.3 The inherited disorders of fibrinogen are afibrinogenemia, hypofibrinogenemia, and dysfibrinogenemia. These conditions are rare and are marked by hematomas, hemorrhage, and ecchymoses depending upon severity.
The homozygous disorder, afibrinogenemia, is an autosomal recessive disorder that shows less than 10 mg/dL fibrinogen in the plasma. This small amount of fibrinogen is usually not demonstrable by traditional methods. Infants with afibrinogenemia will show bleeding from the umbilical stump; poor wound healing and spontaneous abortion are also features of this disorder. Laboratory results will show elevated PT, aPTT, thrombin time (TT), reptilase time, and abnormal platelet aggregation with most aggregating agents and elongated bleeding time. Cryoprecipitate and fresh frozen plasma are the replacement products used for medical management of bleeds for these patients.
Hypofibrinogenemia is the heterozygous form of afib-rinogenemia. This disorder is autosomal recessive and patients show between 20 and 100 mg/dL fibrinogen in their plasma. Patients with this disorder may show mild spontaneous bleeding and severe postoperative bleeding. Results of laboratory testing, whether prolonged or normal, will depend on the amount of fibrinogen present.
Alpha chains Beta chains C
Thrombin's Action on Fibrinogen
Gamma chains C
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