A method for determining immunoglobulin gamma (IgG) antibody isotype concentration from biological samples, comprising: (a) in plurality of wells in a microtiter plate, incubating undiluted biological samples containing IgG antibodies with detection reagents, wherein the detection reagents comprise a defined ratio of two or more different target IgG protein isotypes, or fragments thereof, wherein the two or more different target IgG protein isotypes, or fragments thereof, are detectably labeled, wherein the incubating occurs for a time and under conditions to promote even mixing of the detectably labeled target IgG proteins, or fragments thereof, with the IgG antibodies thereof to produce IgG antibody-target IgG protein mixtures in each well of the plurality of wells; (b) incubating the IgG antibody-target IgG protein mixture in each well of the plurality of wells with two or more different IgG isotype-specific populations of capture reagents, wherein each IgG isotype-specific population of capture reagents comprises binding molecules that selectively bind to a different specific IgG protein isotype, wherein the binding molecules in each IgG isotype-specific population of capture reagents are bound to a bead, and wherein each population of capture reagents is separately distinguishable, wherein the incubating is carried out for a time and under conditions to promote binding of the two or more detectably labeled target IgG proteins, or fragments thereof, and the IgG antibodies to the IgG isotype-specific population of capture reagents, to produce IgG isotype-specific binding complexes; and (c) detecting by flow cytometry signal from the IgG isotype-specific binding complexes to determine the concentration of two or more IgG antibody isotypes present in the biological samples, wherein the amount of an IgG antibody isotype present in the biological samples is inversely proportional to the detected signal from the relevant IgG isotype-specific binding complex; wherein the method does not include any wash steps. (a) in plurality of wells in a microtiter plate, incubating undiluted biological samples containing IgG antibodies with detection reagents, wherein the detection reagents comprise a defined ratio of two or more different target IgG protein isotypes, or fragments thereof, wherein the two or more different target IgG protein isotypes, or fragments thereof, are detectably labeled, wherein the incubating occurs for a time and under conditions to promote even mixing of the detectably labeled target IgG proteins, or fragments thereof, with the IgG antibodies thereof to produce IgG antibody-target IgG protein mixtures in each well of the plurality of wells; (b) incubating the IgG antibody-target IgG protein mixture in each well of the plurality of wells with two or more different IgG isotype-specific populations of capture reagents, wherein each IgG isotype-specific population of capture reagents comprises binding molecules that selectively bind to a different specific IgG protein isotype, wherein the binding molecules in each IgG isotype-specific population of capture reagents are bound to a bead, and wherein each population of capture reagents is separately distinguishable, wherein the incubating is carried out for a time and under conditions to promote binding of the two or more detectably labeled target IgG proteins, or fragments thereof, and the IgG antibodies to the IgG isotype-specific population of capture reagents, to produce IgG isotype-specific binding complexes; and (c) detecting by flow cytometry signal from the IgG isotype-specific binding complexes to determine the concentration of two or more IgG antibody isotypes present in the biological samples, wherein the amount of an IgG antibody isotype present in the biological samples is inversely proportional to the detected signal from the relevant IgG isotype-specific binding complex;