Serum fibrinogen; Plasma fibrinogen; Factor I; Fibrinogen
This is a test that measures the amount of fibrinogen in the blood.
How the test is performed
Blood is drawn from a vein, usually on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to 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 band 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.
For an 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.
How to prepare for the test
There is no special preparation needed.
For infants and children:
The preparation you can provide for this test depends on your child’s age, previous experiences, and level of trust. For general information regarding how you can prepare your child, see the following topics:
- infant test or procedure preparation (birth to 1 year)
- toddler test or procedure preparation (1 to 3 years)
- preschooler test or procedure preparation (3 to 6 years)
- schoolage test or procedure preparation (6 to 12 years)
- adolescent test or procedure preparation (12 to 18 years)
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.
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 produced by the liver. Fibrinogen helps stop bleeding by helping blood clots to form. During normal blood clotting:
- Fibrinogen is broken down by an enzyme called thrombin into short fragments of fibrin. Thrombin also activates a substance called Factor XIII.
- Factor XIII helps weave the fibrin fragments into a complex lattice, closing off injured blood-vessel walls.
- Blood platelets attach to the fibrin fragments, clumping together to form blood clots and stop bleeding.
The normal range is 200-400 mg/dl (mg/dl = milligrams per deciliter).
What abnormal results mean
- Lack of fibrinogen production (acquired or from birth)
- Excessive fibrinogen use (as in disseminated intravascular coagulation)
- Fibrinolysis (abnormal breakdown of fibrinogen)
- Hemorrhage with transfusion of blood products deficient in fibrinogen
Additional conditions under which the test may be performed:
- Disseminated intravascular coagulation (DIC)
- Hemophilia A
- Hemophilia B
- Placenta abruptio
What the risks are
- Excessive bleeding
- 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
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.
by Dave R. Roger, M.D.
All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.