Application of time-resolved fluoroimmunoassay (TR-FIA) for the diagnosis of invasive amoebiasis.

A development of solid-phase immunoassay, time-resolved fluoroimmunoassay (TR-FIA), was used for anti-amoebic antibodies. The test used a chelate of the lanthanide europium as label. The long fluorescent life-time and large Stoke's shift of europium chelates permit sensitive detection in a time-resolved fluorimeter. The TR-FIA was compared with counterimmunoelectrophoresis (CIEP), indirect haemagglutination (IHA) and enzyme-linked immunosorbent assay (ELISA) using 61 sera from patients with invasive amoebiasis, 344 sera submitted routinely for amoebic serology without clinical data, 125 sera from patients with diseases other than amoebiasis, and 86 sera from "healthy" individuals. Overall agreement between TR-FIA and ELISA was 97.1%, between TR-FIA and IHA 93.2%, and between TR-FIA and CIEP 94.0%. Sensitivity, specificity and positive and negative predictive values were calculated to compare the 4 diagnostic methods in invasive amoebiasis. TR-FIA showed a higher validity than other methods. The application of such highly detectable labels in immunometric assays promises to open up entirely new areas of research.