Changes

A latex agglutination test is available for fibrin degradation products (FDP). To perform the test, anti-FDP antibodies adsorbed onto latex particles are added to serial dilutions of test serum. If agglutination is seen at a particular dilution, the test is positive. The most dilute sample that agglutinates gives the overall result of the test. Normal values are between 1/4 and 1/16.

A latex agglutination test is available for fibrin degradation products (FDP). To perform the test, anti-FDP antibodies adsorbed onto latex particles are added to serial dilutions of test serum. If agglutination is seen at a particular dilution, the test is positive. The most dilute sample that agglutinates gives the overall result of the test. Normal values are between 1/4 and 1/16.

Although the test is simple to perform, interpretation may be challenging.  The action of thrombin on fibrinogen is to cleave the protein and produce smaller compounds called fibrinopeptides, plus the fibrin monomer. This monomer polymerizes to form the fibrin gel. The gel is stabilized by the action of factor XIII, activated by thrombin.

Although the test is simple to perform, interpretation may be challenging. This is because other small fragments involved in the homeostasis of fibrinogen and fibrin are measured by the test in addition to ''bona fide'' firbrin degradation products. In general though, an increase in FDP correspons to increased fibrinolysis. This can be due to a local problem of fibrin generation such as thrombosis, trauma or chronic bleeding, or be related to a systemic process, usually DIC³.

 

The action of plasmin is to cleave both fibrinogen and fibrin. Its action is localized by its activation at the site of endothelial rupture, and the tight association of plasminogen and fibrin. The activity on fibrinogen forms small fragments, D and E. The action on fibrin polymer is to form larger fragments. These fragments are anticoagulants formed at the site of coagulation and serve to inhibit the action of thrombin on fibrinogen to form fibrin. Both are also measured by the technique described above.

 

Increased FDP is the laboratory expression of increased fibrinolysis. This may be part of a local problem of fibrin generation such as brain trauma, chronic bleeding, vascular thrombosis, prostate surgery, uterine disorders, or malignancy, or a systemic process, usually DIC. Patients with severe liver disease can have increased fibrinolysis on the basis of poor clearance of circulating plasminogen activators.

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