New enzyme immunoassay of fibrin-fibrinogen degradation products in plasma using a monoclonal antibody.

In several diseases, such as disseminated intravascular coagulation, fibrin-fibrinogen degradation products (FDP) can be detected when serum is used. To avoid the use of serum with the risk of falsely positive and negative results, and to quantitatively measure routinely low levels of FDP in plasma, we developed a solid-phase enzyme immunoassay (EIA), using a monoclonal antibody (No. FDP-14). It reacts specifically with FDP, but not with the parent fibrinogen-fibrin molecule. To raise the monoclonal antibodies we injected into mice a whole mixture of fibrin degradation products isolated after complete lysis of a human blood clot by tissue-type plasminogen activator, because there is a chance that such products resemble FDP in patients' blood more closely than antigens derived from purified fibrinogen. The EIA developed is a two-step assay ("cap-tag procedure"), in which the monoclonal antibody is attached to the wells of microtiter plates. The monoclonal antibody is specific for a neoantigenic determinant in the fragment E moiety, exposed after degradation of fibrinogen-fibrin by plasmin. The assay discriminates neither between degradation products of fibrinogen and fibrin nor between fibrin degradation products that are or are not cross-linked. It is not disturbed by the presence of fibrinogen or fibrin monomer in plasma. The assay is accurate above 60 ng FDP per milliliter and has a detection limit down to approximately 10 ng FDP per milliliter when the supernatant of a lysed blood clot is used as calibration material. In frozen, then thawed plasma specimens from normal individuals, FDP values varied between 30 and 110 ng/ml. Plasma of patients with disseminated intravascular coagulation and of patients receiving thrombolytic therapy had increased FDP values. In patients with ovarian carcinoma, FDP concentrations in plasma varied with the clinical course of the disease. Results indicate that the EIA for FDP in plasma is promising as a diagnostic tool in different clinical situations.