Evaluation of an enzyme-linked immunoassay for the detection in serum of antibodies to Entamoeba histolytica.

A commercially available enzyme-linked immunoassay (ELISA) was compared to an indirect hemagglutination test (IHA) for the detection of antibodies to Entamoeba histolytica on 225 patients' serums. All of the 107 serums that had IHA titers of < 32 (interpreted as excluding the presence of invasive amebiasis) were ELISA negative. Sixty-three of 68 (93%) serums that had IHA titers of > or = 128 (interpreted as indicative of the presence of active or recent infection) were ELISA positive. Fifty serums had IHA titers of 32 or 64 that were considered "equivocal," and the ELISA results for these were: six positive, 35 negative, and nine "intermediate" (optical density values between the arbitrary positive cutoff and the low positive control). It was concluded that "intermediate" (and negative) ELISA results should be interpreted as excluding the presence of invasive amebiasis. Using these criteria, the results obtained with this ELISA appear to compare favorably with those of the "gold standard" IHA. Therefore, this ELISA provides a reliable alternative to the IHA for the serologic diagnosis of amebiasis, which may be advantageous for some laboratories in terms of lower cost, shorter test time, and improved efficiency.