Abstract: This invention relates to bioassay method wherein the presence of a specific soluble antibody in a sample of a bodily fluid, plasma or serum, of an animal, including human, is qualitatively and/or quantitatively determined. The method employs, a first group labelled with an energy donor and a second group labelled with an energy acceptor; the first group, or second group, comprising an antigen of the soluble antibody and the second group, or first group, respectively, comprising a Fab binding moiety capable of binding to a Fab region of antibodies of said animal. The donor and the acceptor form an energy transfer pair capable of energy transfer. The invention further comprises a kit for the bioassay method.

Abstract: This invention relates to bioassay method wherein the presence of a specific soluble antibody in a sample of a bodily fluid, preferably plasma or serum, of an animal, including human, is qualitatively and/or quantitatively determined. The method employs, a first group labelled with an energy donor and a second group labelled with an energy acceptor; the first group, or second group, comprising an antigen of the soluble antibody and the second group, or first group, respectively, comprising a Fab binding moiety capable of binding to a Fab region of antibodies of said animal. The donor and the acceptor form an energy transfer pair capable of energy transfer. The invention further comprises a kit for the bioassay method.