The serological diagnosis of human clonorchiasis by time-resolved fluoroimmunoassay based on GST2-specific IgG4 detection.
Due to its delayed fluorescence of a lanthanide chelate, high accuracy and low background the broad linear range, long fluorescent life-time and large Stokes shift of europium chelates, the time-resolved fluorescence has been developed for higher sensitive immunoassay. In this article, a simple, sensitive and specific method-time-resolved fluoroimmunoassay (TRFIA) was adopted for immunoassay of clonorchiasis, and recombinant glutathione transferases 2 of Clonorchis sinensis (rCsGST2) was used as a diagnostic antigen. To evaluate this novel assay for clinical applications, 409 serum samples were investigated. The diagnostic accuracy of the antigen was evaluated by receiver-operating characteristic (ROC) analysis. The area under the ROC curve (AUC) was 0.965, 95 % confidence interval (CI, 0.946, 0.985). To eliminate the random influence of ambient temperature, test parameters, photometric instruments and so on, the cut-off value was expressed as ratios between the fluorescence of sample and that of a well-defined negative control serum, and the deduced cut-off value was 9.3605. At the optimum cut-off criteria, the technique has a sensitivity of 95.80 %, specificity of 93.60 %. And the cross reactivity revealed that its cross reactivity with Schistosoma japonicum, round worm, hook worm, whip worm, and Toxoplasma gondii was 9.3, 8.3, 7.6, 9.8, and 5.0 %, respectively. Kappa score of agreement between TRFIA and microscopic examination of stools was 0.892, P?0.05. These combined results showed that our method is feasible and could be used for the clinical determination of clonorchiasis.