Fibrin degradation products (FDPs) are generated through the proteolytic breakdown of fibrinogen or fibrin by plasmin. To measure FDPs, a blood sample is first collected in a tube containing thrombin, which facilitates the conversion of fibrinogen into a clot, thereby removing it from the sample. Additionally, soybean trypsin inhibitor is used to inhibit plasmin activity, preventing the in vitro degradation of fibrin.
The test procedure involves mixing a suspension of latex particles, which are conjugated with antifibrinogen antibodies (or fragments D and E), with serial dilutions of the patient's serum on a glass slide. The presence of FDPs is indicated by agglutination of the latex particles, as shown in Figure 1. The highest serum dilution at which agglutination is observed is used to determine the concentration of FDPs in the sample.
Elevated levels of FDPs are indicative of fibrinogenolysis or fibrinolysis, which can occur in conditions such as disseminated intravascular coagulation, deep venous thrombosis, severe pneumonia, and recent myocardial infarction. This test is critical for diagnosing and monitoring these conditions.