Inconclusive results in conventional serological screening for Chagas' disease in blood banks: evaluation of cellular and humoral response.
OBJECTIVE
To find the most reliable screening method for Trypanosoma cruzi infection in blood banks.


METHODS
Epidemiological data, lymphoproliferation assay, parasitological, conventional serological tests: immunofluorescence, haemagglutination, ELISA with epimastigote and trypomastigote antigens and reference serological tests: trypomastigote excreted-secreted antigens (TESA) blot and chemiluminescent ELISA assay with mucine from trypomastigote forms were applied to individuals with inconclusive serology, non-chagasic individuals and chronic chagasic patients.


RESULTS
TESA blot had the best performance when used as a single test in all the groups. In the inconclusive group 20.5% of individuals were positive for TESA blot, 23.3% for either lymphoproliferation or TESA blot, and 17.8% for lymphoproliferation only. Positive lymphoproliferation without detectable antibodies was observed in 5.47% of all inconclusive serology cases. Analysis of six parameters (three serological assays, at least one parasitological test, one lymphoproliferation assay and epidemiological data) in the inconclusive group showed that diagnosis of Chagas' disease was probable in 15 patients who were positive by two or more serological tests or for whom three of those six parameters were positive.


CONCLUSIONS
TESA blot is a good confirmatory test for Chagas' disease in the inconclusive group. Although lymphoproliferation suggests the diagnosis of Chagas' disease in the absence of antibodies when associated with a high epidemiological risk of acquiring Chagas' disease, the data from this study and the characteristics of the lymphoproliferation assay (which is both laborious and time-consuming) do not support its use as a confirmatory test in blood-bank screening. However, our findings underscore the need to develop alternative methods that are not based on antibody detection to improve the diagnosis when serological tests are inconclusive.
Furuchó
Celia Regina
CR
Laboratório de Investigação Médica cm Imunologia, Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo, São Paulo, Brazil. celiarf@usp.br
Umezawa
Eufrozina S
ES
Almeida
Igor
I
Freitas
Vera L
VL
Bezerra
Rita
R
Nunes
Elisabete V
EV
Sanches
Maria C
MC
Guastini
Cristina M
CM
Teixeira
Antonio R
AR
Shikanai-Yasuda
Maria A
MA
D000328:Adult; D000368:Aged; D000818:Animals; D001681:Biological Assay / Q000379:methods; D001771:Blood Banks; D001938:Brazil; D049109:Cell Proliferation; D014355:Chagas Disease / Q000175:diagnosis* / Q000276:immunology; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D006801:Humans; D015151:Immunoblotting / Q000379:methods; D008214:Lymphocytes / Q000502:physiology; D008875:Middle Aged; D012680:Sensitivity and Specificity; D012698:Serologic Tests / Q000706:statistics & numerical data*; D014349:Trypanosoma cruzi / Q000276:immunology; D055815:Young Adult