Enhanced sensitivity agglutination assays multivalent ligands

A competitive agglutination method to detect and/or quantitate an analyte in a sample which comprises:

• (A) incubating
• (a) a sample suspected of containing said analyte,
• (b) a carrier reagent which comprises a specific binding substance attached to a particle, wherein said specific binding substance specifically binds to a non-particulate agglutinating agent,
• (c) the non-particulate agglutinating agent which comprises at least two common binding sites which specifically bind the specific binding substance of the carrier reagent, the analyte, and a soluble multivalent ligand,
• (d) the soluble multivalent ligand which comprises at least two binding sites which specifically bind the common binding sites of the non-particulate agglutinating agent and which are joined by a linking group of sufficient length to permit binding of the multivalent ligand with at least two units of the non-particulate agglutinating agent, wherein said soluble multivalent ligand 1) does not specifically bind to the specific binding substance of the carrier reagent and 2) is present in a concentration below that which would interfere with an agglutination reaction,
• wherein the analyte competes with the carrier reagent for the common specific binding sites on the non-particulate agglutinating agent, thus reducing the extent of agglutination;
• (B) detecting or measuring the resulting agglutination;
• and
• (C) relating the extent of inhibition of agglutination resulting from the presence of analyte in the sample to the presence and/or amount of the analyte.