Reducing interference in ligand-receptor binding assays

In an assay method for a ligand which is a member of a specific binding pair ("sbp member") consisting of said ligand and its complementary receptor wherein said ligand has a binding site in common with a binding site of an interfering substance having at least two binding sites, said method employing a receptor recognizing the common binding site, the improvement which comprises adding to an assay medium containing said analyte and said interfering substance, without intervening separation, a specific binding compound which blocks the binding between said receptor and said interfering substance and does not block the binding between said receptor and ligand.

In an assay method for an antigen which is a member of a specific binding pair ("sbp member") consisting of said antigen and its complementary antibody wherein said antigen has at least two epitopic sites, one of said epitopic sites being common to an interfering substance having at least two epitopic sites, said method employing a common antibody, said common antibody recognizing the common epitopic site,

• the improvement which comprises combining with an assay medium containing said antigen and said interfering substance an amount of a blocking antibody sufficient to block the binding between said common antibody and said intefering substance wherein said blocking antibody does not block the binding between said common antibody and said antigen.

In an assay method for a protein analyte having alpha and beta sub-units, wherein one of said sub-units is common to a sub-unit of an interfering protein having alpha and beta sub-units, said method employing a common antibody which recognizes the sub-unit common to said protein analyte and said interfering substance and an antibody specific for the non-common sub-unit of said analyte, the improvement which comprises combinine with said assay medium containing said interfering substance an amount of a blocking antibody that binds specifically to said interfering subtance but not to its separate alpha and beta sub-units, said blocking antibody blocking the binding of said interfering substance to said common antibody.

A composition comprising one or both of (1) a common receptor that specifically binds to a binding site common to an endogenous interfering substance and a ligand suspected of being present in a sample and (2) members of a signal producing system capable of producing a detectible signal in the presence of said ligand in combination with (3) an amount of a blocking receptor which does not bind to said ligand and does bind to said endogenous interfering substance and thereby blocks the binding between said common receptor and said endogenous interfering substance.