Standardization of serological tests for Chagas disease: an immunoenzymatic test for blood donors triage

Abstract

In the serological diagnosis of Chagas disease large divergences may be found even between laboratories with experience, as a consequence of different criteria for the standardization of the tests. To standardize a immunoenzymatic test developed primarily for screening blood donors, serum panels were carefully chosen so as to best represent chagasic and non-chagasic populations. Produced for the highest sensibility and stability, the new reagent (bioELISA cruzi, Biolab Diagnóstica S/A, Brasil), was tested in serum from 1648 patients 219 with Chagas disease and 104 with other diseases, plus a comparison with well standardized immunofluorescence and hemagglutination tests in 1325 sera. In the immunoenzymatic assays, the cut off was indicated by the absorbance value of a chagasic serum showing a minimal reactivity. ELISA sensibility was 0.9954 and specificity 0.9969, as co-negativity. False positive results were absent with sera from syphilis, toxoplasmosis, mononucleosis and high titered sera for antistreptolysin 0 antibodies. However they were seen in 5 to 15 cases of tegumentar leishmaniasis, 1 of 12 Kala-azar 1 of 15 rheumatoid arthritis and 1 of 12 systemic lupus erythematosus. The high sensibility in chagasics and high specificity in the general population indicate the confiability of the immunoenzymatic assay for screening blood donors and even to confirm a clinical diagnosis of Chagas' disease.