Comparison of methods for detecting soluble fibrin in plasma. An in vitro study

The ability of the COA-SET Fibrin monomer (COA-SET FM) test to detect soluble fibrin was evaluated by comparing the results of the COA-SET FM test with fibrino-peptide A (FPA) determinations following thrombin incubation of plasma or whole blood. In addition, two semiquantitative tests (erytrocytes-agglutination test (FM-test) and ethanol gelation test (EGT)) were included in the study. Under the experimental conditions used, the COA-SET FM test proved less sensitive than the FPA-assay. There was a strong correlation between the results obtained by the two tests (r=0.86, p=0.0001). When solely regarding low levels of soluble fibrin, however, the correlation was weaker (r=0.59, p=0.0003). The FM-test was less sensitive than the COA-SET FM test, but more sensitive than EGT at normal and low fibrinogen concentrations. At high fibrinogen concentrations, however, EGT proved more sensitive than the FM-test. Knowing that 1–2 moles of FPA are released per mole of fibrin monomers formed, a discrepancy was observed between the FPA concentrations and the fibrin monomer concentrations as determined by the COA-SET FM test, the FPA levels being 2–25 times higher than the fibrin monomer levels. The discrepancy was greatest at incipient fibrinogen-fibrin transformation and at high plasma fibrinogen levels. This may suggest that fibrinogen in some way interfered with the stimulating effect of fibrin on the t-PA catalyzed activation of plasminogen, the principle upon which the COA-SET FM test is based. In addition, the way of preparing fibrin monomers might influence their properties as plasminogen activators and contribute to the discrepancy. Further studies are in progress to clarify these matters.