FDPs are fragments produced by proteolytic digestion of fibrinogen or fibrin by plasmin. For determination of FDPs, blood is collected in a tube containing thrombin (to remove all fibrinogen by converting it into a clot) and soybean trypsin inhibitor (to inhibit plasmin and thus prevent in vitro breakdown of fibrin). A suspension of latex particles linked to antifibrinogen antibodies (or fragments D and E) is mixed with dilutions of patient’s serum on a glass slide. If FDPs are present, agglutination of latex particles occurs (see Figure 814.1). The highest dilution of serum at which agglutination is detected is used to determine concentration of FDPs. Increased levels of FDPs occur in fibrinogenolysis or fibrinolysis. This occurs in disseminated intravascular coagulation, deep venous thrombosis, severe pneumonia, and recent myocardial infarction.
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