Plasma Fibrinogen

Fibrinogen (factor I) originates in the liver and is converted to fibrin during clotting. Because fibrin is necessary for clot formation, fibrinogen deficiency can produce mild-to-severe bleeding disorders.

This test is used to determine the amount of fibrinogen present in a blood sample. Note that fibrinogen deficiency may also be indicated by prolonged activated partial thromboplastin time, prothrombin time, and thrombin time.

Purpose

• To aid the diagnosis of suspected clotting or bleeding disorders caused by fibrinogen abnormalities

Patient preparation

• Explain to the patient that this test is used to determine if blood clots normally.
• Tell him that a blood sample will be taken. Explain who will perform the venipuncture and when.
• Reassure him that drawing a blood sample will take less than 3 minutes.
• Explain that he may feel slight discomfort from the tourniquet pressure and the needle puncture.
• Check patient history for use of heparin or oral contraceptives and notify the laboratory if these drugs are in use.
• Inform the patient that food or fluids need not be restricted before the test.

Procedure and posttest care

• Perform a venipuncture, and collect the sample in a 7-ml blue-top tube.
• Completely fill the collection tube, invert it gently several times, and send it to the laboratory immediately, or place it on ice.
• Avoid excessive probing during venipuncture, and handle the sample gently.
• If a hematoma develops at the venipuncture site, apply warm soaks.

Precautions

• This test is contraindicated in patients with active bleeding and acute infection or illness, and in those who have received blood transfusions with­in 4 weeks.

Reference values

Abnormal findings

Depressed fibrinogen levels may indicate congenital afibrinogenemia; hypofibrinogenemia or dysfibrinogenemia; disseminated intravascular coagulation; fibrinolysis; severe hepatic disease; cancer of the prostate, pancreas, or lung; or bone marrow lesions. Obstetric complications or trauma may cause low levels.

Markedly decreased fibrinogen levels impede the accurate interpretation of coagulation tests that have a fibrin clot as an end point.

Elevated levels may indicate cancer of the stomach, breast, or kidney, or inflammatory disorders, such as pneumonia or membranoproliferative glomerulonephritis.

Interfering factors

• Failure to fill the collection tube completely, to adequately mix the sample and anticoagulant, or to send the sample to the laboratory promptly.
• Hemolysis due to excessive probing at the venipuncture site or to rough handling of the sample.
• Third trimester of pregnancy and postoperative status (possible increase).
• Fibrinogen inhibitors, such as strep­tokinase.
• Acute infection.
• Transfusion of whole blood, plasma, or fractions within 4 weeks before the test.

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