Effect of Fluosol-DA on radioimmunoassay results

Fluosol-DA, an emulsion of perfluorocarbons, is used as a blood substitute. Its presence in samples affects results of certain radioimmunoassays routinely done in our laboratory. In several, added Fluosol-DA caused an upward displacement of the standard curve, the extent of which depended on the structure and quantity of the assayed antigen, the concentration of Fluosol-DA, and the nature of the immunoreagents. Fluosol-DA markedly affected results of assays for triiodothyronine, thyroxin, and digoxin (by one method), but assays for aminoglycosides and protein hormones were unaffected. We determined that Fluosol-DA interacts with unbound labeled (and, presumably, with unlabeled) antigen to form a complex that coprecipitates with the bound antigen-antibody fraction during the separation step. In comparison with the idealized condition we observed an apparent increase in antibody-bound labeled antigen and consequently an apparent underestimation of the measured antigen. Depending on the nature of the immunoreagents, antibodies can extract more or less of their respective antigens from particles of Fluosol-DA emulsion.