Sensibilidade e especificidade dos testes sorológicos para doença de Chagas usados na triagem sorológica de doadores de sangue.

Abstract

Justification and purpose: Currently, one of the biggest problems in the serological screening of blood donors in respect to Chagas disease is the occurrence of indeterminate reactions, what makes to many healthy individuals as owners of a serious illness. This paper aims to evaluate the serological profile of Chagas disease of donors at Uberaba Blood Center and the sensitivity and the specificity of the employed tests. Casuistry and Methods: The work was carried out through the analysis of descriptions of blood donors that had appeared in the Uberaba Blood Center between the years 2000 to 2005, of which were collected partner-demographic data. Of the 95,990 donations carried through in this period, 269 had presented not negative serology for Chagas disease. Of these, 30 positive and 30 indeterminate blood donors were convoked for the repetition of serological tests (ELISA, HAI and IFI), accomplished of a parasitological test and an epidemiologic evaluation. It was also analyzed a group of negative donors concerning Chagas disease (control group). The statistics analysis was made through descriptive statistics, tests of comparison of proportions (z) and chi-square (X2), calculations of the coefficients of sensitivity and specificity and Kappa index for the analysis of agreement among the tests. Results: The occurrence of not negative donors for Chagas disease at Uberaba Blood Center it was of 0,28% in the last six years. Concerning the partner-demographic characteristics, in the group of the positives there was predominance of first-time donors (99%), whites (66%), over 30-year-old (81%), originary at endemic regions (96%) and carrying out low-qualified professions (43%). It was observed that among the 30 donors with undetermined serology, 28 (93%) presented negative results in the four tests carried out, one was positive in the ELISA test and the other remained indeterminate for the HAI technique. The set of tests that presented the best agreement was ELISA x HAI (Kappa= 0,66).The repetition of the serological techniques disclosed 100% of sensitivity for the three serological tests and specificity of 96,6% for ELISA and 100% for HAI and IFI. Conclusion: The occurrence of undetermined serological reactions among blood donors, despite relatively low as it shows our study, strengthens the necessity to persist in the search for alternative laboratorial methods, of low cost and high reproducibility, with sensitivity and specificity of 100% and that can be used in association with serological tests, aiming to compensate the possible imperfections of these tests. This would protect the receiver of the transfusion of chagasic blood and would eliminate the false-positive reactions, thus preventing the wastefulness of blood bags and the exclusion of falsely inapt donors.