COAGULO-RADIOIMMUNOMETRIC ASSAY FOR THE QUANTITATION OF FIBRIN MONOMER IN HUMAN-PLASMA - PRINCIPLES AND DEVELOPMENT OF THE METHOD

When a mixture of 125I-labeled human fibrin monomer (HFM) and human plasma or purified fibrinogen (HFg) is added to insolubilized bovine fragment D (BFD-Sepharose), the amount of HFM which binds to BFD-Sepharose is proportional to the amount of HFM and BFD-Sepharose and inversely proportional to the amount of fibrinogen in the test tube. With 15-fold molar excess of insolubilized BFD over HFg and 2 to 10 percent of HFM (compared to HFg) in the test system about 25 percent of the HFM binds to insolubilized BFD. The distribution ratio of labeled HFM is however almost independent of the concentration of HFM, and can therefore not be used to quantitate HFM in plasma. When purified 131I-labeled antibodies to HFg are added to BFD-Sepharose to which 125I-labeled HFM is bound, the binding of 131I is proportional to the amount of HFM on the gel. This indicates that labeled antibodies can be used to quantitate HFM bound to BFD-Sepharose. Under the experimental conditions studied (20 μl plasma containing 50 μg HFg and 0 to 5 μg HFM incubated with 0.25 mg insolubilized BFD), 0.6 - 0.8 percent of the plasma fibrin(ogen) and 25 percent of the HFM bind to the gel. Thus addition of 3 percent HFM to plasma results in a doubling of the amount of 131I-labeled anti-HFg Ig bound to BFD-Sepharose. This test tube method for the quantitation of HFM in plasma has an analysis time of about 5 hours in its present version and a large number of samples can be handled at the same time. It may therefore constitute a useful alternative to the affinity chromatographic method for measuring HFM in plasma. © 1979.