Radioimmunoassay of FDP (No. 2)

Abstract

Fibrinogen and fibrin degradation products, fragment D (Fg D) and fragment E (Fg E), were measured in human serum by radioimmunoassay (RIA) technique.
Fibrinogen was digested for five hours by plasmin to obtain Fg D and Fg E as the major products.
Technique for separating these fragments from each other and from larger fragments (Fg X, Fg Y) present in the crude digest, comprise gelfiltration with Sephadex G-200 and isoelectric fractionation which gave satisfactory purity and efficiency for preparative purpose.
A sensitive 2-sites immunoradiometric assay for FDP was newly developed using paper discs as solid phase.
Detection limit of this method was 1ng/ml.
In six healthy subjects, the serum levels ranged from 108 to 260ng/ml for Fg D, and from 60 to 120ng/ml for Fg E.
Both raised levels were found in the patients with disseminated intravascular coagulation of hepatoma, gastric cancer, AML, APL and CML.
Advantages of RIA system over tanned red cell haemagglutination inhibition immunoassay was its sensitivity.
There is, however, a possibility that RIA of FgDP is detecting residual fibrinogen in the serum, since anti-FgDP antiserum showed weak cross-reaction to fibrinogen by double immunodiffusion test.
In order to eliminate interference by residual fibrinogen in the serum, antiserum against FgDP was further purified by affinity chromatography to remove antifibrinogen activity.
Thus purified antibody exhibited no crossreaction to fibrinogen by RIA method, and showed nonprecipitable property in double immunodiffusion test using 1% Agar which contains 4% polyethylene glycol.
By using this antibody, FDP in plasma was detectable, thus eliminating the possibility of coprecipitation of FDP with blood clot when serum was collected.