Evaluation of an enzyme-linked immunosorbent assay in the serodiagnosis of amoebic liver abscess

An indirect enzyme-linked immunosorbent assay (ELISA) was evaluated for the detection of anti-amoebic IgG and IgM antibodies to assess its value in distinguishing past from current infection in invasive amoebiasis, particularly in amoebic liver abscess (ALA) patients. Using sera from 295 individuals, the ELISA was also compared with the amoebic gel diffusion (AGD) test. In 100 patients the IgG-ELISA at a single test dilution of 1/6,400 had a sensitivity of 99% for clinically diagnosed ALA. In these same patients the IgM-ELISA at a single dilution of 1/400, had a sensitivity of 64% and a specificity of 97.9%. No cross-reactions were observed in sera from patients with collagen vascular disease. In 121 patients without clinical invasive amoebiasis, 8 were AGD-positive and 12 were IgG-ELISA-positive, giving the latter assay a specificity of 91.7%. This is thought to be due to past infection with Entamoeba histolytica. In symptomless carriers of pathogenic zymodemes, 10/11 were seropositive by the IgG-ELISA and 11/11 by the AGD test. There was an excellent correlation between the IgG-ELISA and the AGD test (r = 0.99). The IgG-ELISA is a sensitive, specific, simple and rapid test. It has the clinical advantage that results are obtainable 2 1/2 hours after receipt of the specimen, compared with the 24-48 hours required for the AGD test. The prompt availability of IgG-ELISA results could prove advantageous for implementation of early therapy. The IgM-ELISA was not found to be sensitive enough to be used as an index of active amoebic infection.