| Definition: |
A test that measures the amount of fibrinogen in the blood.
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| Alternative Names: |
Serum fibrinogen; Plasma fibrinogen; Factor I; Hypofibrinogenemia test
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| How the test is performed: |
Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
Infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
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| How to prepare for the test: |
Adult:
There is no special preparation.
Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
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| How the test will feel: |
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
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| Why the test is performed: |
This test may be performed when abnormal blood clotting is present, particularly if there is excessive bleeding.
Fibrinogen is a protein synthesized by the liver. It is the substance used in the blood to form a clot. Fibrinogen is cleaved (broken) by the enzymethrombin to form fibrin peptides (short protein fragments) during normal coagulation (blood clotting). Thrombin also activates fibrin stabilizing factor (Factor XIII) which subsequently cross-links the fibrin into a complex lattice, closing off injured blood vessel walls. Platelet aggregation at the site of injury is facilitated by binding of protein receptors in the platelet cell membranes to fibrin peptides.
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| Normal Values: |
The normal range is 200 to 400 mg/dl.
Note: mg/dl = milligrams per deciliter
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| What abnormal results mean: |
- lack of fibrinogen production (acquired or congenital)
- excessive fibrinogen utilization (as in disseminated intravascular coagulation)
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fibrinolysis, or abnormal breakdown of fibrinogen (either primary or secondary)
- hemorrhage, with transfusion of blood products deficient in fibrinogen
Additional conditions under which the test may be performed:
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| What the risks are: |
- excessive bleeding
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fainting or feeling light-headed
- hematoma (blood accumulating under the skin)
- infection (a slight risk any time the skin is broken)
- multiple punctures to locate veins
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| Special considerations: |
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
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