A turbidimetric assay for quantitating functional fibrin(ogen) using polystyrene-divinylbenzene microparticles

A sensitive assay has been developed to quantitate fibrinogen in plasma or in other aqueous solutions. Microscopic latex particles, modified with a mixed monomolecular film of lecithin and fibrinogen, are used as a solid-phase reagent. These lecithin/fibrinogen-coated beads aggregate when stirred in the presence of thrombin and, when solution-phase fibrinogen is added, the increased rate of aggregation is proportional to the concentration of soluble fibrinogen. Using a sample volume of 200 microl, as little as 15 nM ( approximately 5 microg ml-1) fibrinogen can be measured. Fibrinogen determinations using the bead assay compared favorably with those derived from a standard clinical assay, with a correlation coefficient (r2) of 0.9710 over a range of 2.5 to 28.0 microM. Analytic precision was comparable to available assays, with typical coefficients of variation of 12.7 and 7.1% for fibrinogen concentrations of 30 nM and 15.0 microM, respectively. The method has a dynamic range of 15 nM to over 3.0 microM and offers the advantage of being sensitive to 20-fold lower concentrations of fibrinogen compared to routine clot-based methods. Unlike immunological assays, e.g., ELISA, it measures only the functional protein. This bead method should prove to be of greatest use to investigators measuring low levels of functional fibrin(ogen).