An indirect immunofluorescent test for human antibodies to tetanus toxoid using an insoluble toxoid as antigen.

An indirect fluorescent antibody (FA) test for detection of human antibodies to tetanus toxoid is described using an ethylchloroformate-prepared polymer of tetanus toxoid as the particulate slide test antigen. Titres of the FA test were compared with those obtained with the toxin neutralization (TN) test in mice. No antisera were FA-positive at less than 0-0025 AU/ml. Positive correlation of the FA test with the TN test was 50% between 0-0025 and 0-01 antitoxin units/ml (AU/ml) and 100% between 0-02 and 160 AU/ml. In general, an increase in FA titres correlated with an increase in TN titres beginning at about 0-08-0-16 AU/ml.