Equis ISSN 2398-2977

Plasma: fibrinogen

Overview

• Fibrinogen: soluble plasma protein produced in hepatic parenchymal cells and stored until required.
• Free in blood normally accounting for approximately 5% of plasma protein.
• Acute phase reactant protein detectable from 48 hours after onset of inflammation and reaching peak levels within 5-7 days.
• Inflammation (bacterial, chemical, neoplastic, traumatic) increases [fibrinogen]. Increase temporary if acute, but may persist in chronic inflammation.
• Used in blood coagulation therefore decreases [fibrinogen] in disseminated intravascular coagulation (DIC)   Disseminated intravascular coagulation  and following major trauma/surgery.

Sampling

Tests

Methodologies

• Thrombin + plasma   →   fibrin clot which is washed, dried and weighed. Time consuming and may be adversely affected by large amounts of heparin .

Turbidometric method

• Plasma + ammonium sulphate   →   precipitated fibrinogen   →   resulting turbidity measured photometrically.

Immunologic method

• Antifibrinogen is complexed with latex particles and mixed with diluted blood. Agglutination occurs at [fibrinogen] >10 g/l.
• Rapid, easy but not quantitative and does not differentiate fibrinogen from its breakdown products.

Thrombin time

• Measures plasma [functional fibrinogen]. Citrate anticoagulated plasma + thrombin   →   clotting; the time to reach standardized clotting is proportional to fibrinogen concentration.

Heat precipitation method

• EDTA + whole blood drawn into 2 microhematocrit tubes   →   tubes sealed at one end   →   centrifuge for 5 minutes in microhematocrit centrifuge   →   place one tube in water bath at 56°C for 3 minutes then centrifuge. Read total plasma protein (TPP) by refractometry for both tubes. The difference between the two results equals the fibrinogen concentration in grams/dl.

Availability

• All commercial laboratories.
• Some practice laboratories.

Validity

Sensitivity

• Sensitive.

Specificity

• Low specificity.

Predictive value

• Best used as part of a blood profile.

Technique (intrinsic) limitations

• Does not provide specific diagnoses.

Result Data