Detection of tetanus antitoxin using Eu(3+)-labeled anti-human immunoglobulin G monoclonal antibodies in a time-resolved fluorescence immunoassay.

Tetanus antitoxin in human sera was detected with solid-phase immunoassays in microtitration modules coated with tetanus toxoid by using Eu(3+)-labeled anti-human monoclonal antibodies on the basis of an exactly calibrated antibody standard. The use of a time-resolved fluorescence immunoassay (TR-FIA) significantly improved the quantitative detection of tetanus antitoxin over that of the enzyme-linked immunosorbent assay (ELISA) technique because of its high sensitivity and its wide measurement range, detecting antibody levels between 0.001 and 12.5 IU/ml with a single serum dilution of 1:100. For the same purpose, two different serum dilutions (1:100 and 1:1,000) were needed in the ELISA technique. TR-FIA is reproducible and can be performed in 3.5 h. A study of 2,630 serum samples was undertaken to examine the age-dependent distribution of titer levels, indicating the decline of sufficient protection in patients older than 60 years. The wide measurement range of TR-FIA enabled fast examination of large numbers of serum samples without the need for repetition, with further sample dilution, as was often necessary in the ELISA procedure.