Radioimmunoassay of fragment E-related neoantigen: validation studies and clinical application

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Summary. Measurement of fibrinogen-fibrin degradation products (FDP) levels in plasma may provide a direct index of plasmin action, and increased levels of FDP would indicate coagulopathy. We have established an E-neoantigen radioimmunoassay (Eneo RIA) that can determine normal and pathological plasma levels of E-related FDP. The assay employs rabbit antiserum produced against fragment E derived from a plasmin digest of fibrinogen and subsequently absorbed with fibrinogen. The absorbed antiserum contains antibodies which are equally reactive with fibrinogen derived E (Fg-E) and fibrin derived E (Fb-E) but not with fibrinogen at 1 mg/ml. The Eneo RIA was validated by assay parallelism and by recovery experiments. Plasma Eneo immunoreactivities in 14 normals were 4–22 ng/ml (mean 12.7 ng/ml). Plasma Eneo levels in 23 of 24 patients with neoplastic and haematological diseases were elevated above normal (range 27–2027 ng/ml). Unusually high Eneo values were observed with three patients whose diseases were complicated by either disseminated intravascular coagulation (DIC) or deep vein thrombosis. After heparin therapy, the Eneo level of a patient with chronic DIC declined. A pathological plasma was eluted from a Sephadex G-200 column and Eneo immunoreactivity was determined on the eluates. The gel filtration pattern of Eneo indicates that E-related FDP is a family of plasmic fragments derived from crosslinked fibrin.