[Screening for Chagas disease by immunoenzymology: comparison of ELISA with immunofluorescence and indirect hemagglutination in 976 blood donors].

The efficiency of an immunoenzymatic technique (ELISA) for the systematic research of Chagas' disease in blood donors was compared with one of 2 well-known methods, indirect haemagglutination (IHA) and indirect fluoro immuno assay (IFA). For the ELISA technique two different antigenic extracts from epimastigote culture forms of T. cruzi, were used for sensitizing the polystyrene plates: a crude extract (Ag R) and a delipidized one (Ag B). Firstly the authors tested these 3 techniques in 5 control groups: sera from Chagas' disease, negative control sera, sera from visceral leishmaniasis, african trypanosomiasis and finally monoclonal gammapathies, the high levels of blood proteins being a possible cause of false positives. Secondly the screening of Chagas' disease was performed in the same way in 976 blood donors from Recife, Brazil. In the case of the Ag-R extract used in the ELISA technique a high cross-reactivity was found with visceral leishmaniasis sera, along a risk of false positives with gammapathic ones. The sensitivity of this technique was found to be high (3,3 +/- 1 p. cent of positive blood donors) and a very good correlation was found with the reference techniques, IFA and IHA, the sensitivity of which is lower (2,3 +/- 1 and 1,7 +/- p. cent). The use of a delipidized antigenic extract (Ag B) for the ELISA technique is not suitable, in spite of an apparent higher specificity: indeed, the positives rate is high (11,5 +/- 0,2 p. cent), but the correlation is very weak or non existent in the case of IHA or IFA. In conclusion, the ELISA technique using a crude extract of T. cruzi appears to be a very convenient method for screening blood donors with Chagas' disease, the lack of specificity due to leishmaniasis or monoclonal blood proteins not posing any real problem to blood banking.