In the common final pathway, fibrinogen (factor I) is converted to fibrin by thrombin (see Fig. 2-1). Plasma fibrinogen studies are based on the fact that, in normal healthy individuals, the serum should contain no residual fibrinogen after clotting has occurred.

Three different techniques can be used to perform the test: (1) standard assay (classical procedure), (2) immunologic technique, and (3) heat-precipitation tests. In the standard assay, thrombin is added to the blood sample to induce clotting. Because fibrinogen is a plasma protein, the amount of protein in the resulting clot is measured. The quantity of precursor fibrinogen present is then extrapolated from this value. In the immunologic technique, the degree of reactivity between the plasma sample and antifibrinogen antibodies is measured. The assumption underlying this method is that any plasma constituent that reacts with antifibrinogen antibodies is, indeed, fibrinogen. Heat-precipitation tests are based on a similar assumption that all of the material responsive to the precipitation technique is really fibrinogen.³⁴

• 150-450 mg/dL

• Transfusions of whole blood, plasma, or fractions within 4 weeks of the test may lead to erroneous results.
• Traumatic venipuncture and excessive agitation of the sample may alter test results.

• Confirmation of suspected DIC, as indicated by decreased fibrinogen levels
• Evaluation of congenital or acquired dysfibrinogenemias
• Monitoring of hemostasis in disorders associated with low fibrinogen levels (e.g., severe liver diseases and cancer of the prostate, lung, or pancreas)
• Detection of elevated fibrinogen levels, which may predispose to excessive thrombosis in various situations (e.g., immune disorders of connective tissue; glomerulonephritis; oral contraceptive use; cancer of the breast, stomach, or kidney)

Nursing Care Before the Procedure

Client preparation is the same as that for any study involving the collection of a peripheral blood sample (see Appendix I).

• If the individual is receiving anticoagulant therapy, the time and amount of the last dose should be noted.

A venipuncture is performed and the sample collected in a light-blue-topped tube. As with other coagulation studies, traumatic venipunctures and excessive agitation of the sample should be avoided. The sample should be sent to the laboratory immediately.

Nursing Care After the Procedure

Care and assessment after the procedure are essentially the same as for any study involving the collection of a peripheral blood sample.

• Because the client may have a coagulation deficiency, maintain digital pressure directly on the puncture site for 3 to 5 minutes after the needle is withdrawn.
• Inspect the site for excessive bruising after the procedure.