The invention relates to a method of preparing a reagent for the determination by hemagglutination of antibodies to bacterial toxins. According to this method erythrocytes are treated with glutaraldehyde and then with the bacterial toxins in the presence of glutaraldehyde without a wash step. The reagent thus obtained is further treated with a reagent for blocking aldehyde groups.

A column comprising an insoluble carrier and an anti-.beta..sub.2 -microglobulin antibody immobilized to the carrier can specifically adsorb and remove .beta..sub.2 -microglobulin in the blood. This column is useful for the prevention and treatment of diseases such as carpal tunnel syndrome observed in patients undergoing blood dialysis.

A method for the quantification or qualification of antigens with an immunological solid phase method, for example of the ELISA type, during which the invention seeks to overcome the difficulties with falsely high or falsely positive measurement results. This purpose is achieved by exposing two aliquots, preferably of the same size, of the sample containing the antigen that is to be determined to two solid phases with identical anti-antigen-antibody-coated surfaces, in which one exposure (exposure 1) occurs in the presence of antibodies present in the aliquot with the same specificity as the antibodies with which the solid phases are coated, and the other exposure (exposure 2) preferably occurs in the presence of antibodies present in the aliquot with nonspecificity for the antigen in question, but otherwise essentially the same as the antibodies present in the aliquot in exposure 1, and the antigen is quantified by means of the difference between the bonded antigen in exposure 1 and the bonded antigen in exposure 2. The method is also applicable for detecting antibodies.

In an immunoassay, ultrafine particles having an average particle size of 0.2 .mu.m or smaller and sensitized with a substance, which has reactivity with the materials to induce a nonspecific immunoreaction, are added to a sample to inhibit the nonspecific immunoreaction. The above immunoassay can avoid the influence of nonspecific factors more effectively, thereby permitting accurate measuremens on the concentrations of antigens in samples such as blood, urine, body fluid and the like.

The invention teaches a method for improving the ability to determine a polyvalent substance via use of an immunoaggregate during the assay. The immunoaggregate eliminates substances which can lead to incorrect results otherwise.