Immunoassay utilizing alginate to enhance signal to noise ratio

In an immunoassay which comprises forming two specific binding reactions of (1) the first binding of a sample analyte molecule to an antibody immobilized to a solid phase support and (2) the second binding of a labeled antibody to the sample analyte molecule and determining the amount of the signal developed from the label, wherein the improvement resides in subjecting the labeled antibody to the second specific binding reaction to the analyte in the presence of an alginate, at a concentration of about 0.1% to 0.5% a partially hydrolyzed alginate, or a mixture thereof at a concentration of about 0.1% to 10%.