Detection of antibodies to tetanus toxoid: comparison of a direct haemagglutination method with a radioimmunoassay.

Two methods of detecting antibodies to tetanus toxoid were compared, a radioimmunoassay (RIA) employing radiolabelled staphylococcal protein A and a direct haemagglutination (HA) method employing sheep erythrocytes coupled to tetanus toxoid with chromic chloride. These were shown to have a similarly high specificity with the HA method showing slightly higher sensitivity. Haemagglutination offers several additional advantages in terms of simplicity, low cost and less requirement for specialised equipment. The assays were also used to demonstrate a transient IgM response after repeated booster injections with absorbed toxin given to seropositive individuals, and these antibodies were found to be protective in biological tests.