TG-ROC analysis of immunofluorescence assays in canine visceral leishmaniasis diagnosis.
OBJECTIVE
To analyze the accuracy of the diagnosis of two protocols of indirect immunofluorescence assays for canine visceral leishmaniasis.


METHODS
Dogs from the seroepidemiological survey conducted in an endemic area of the cities of Araçatuba and Andradina, in Northwestern São Paulo state, in 2003, and in a non-endemic area of the metropolitan region of São Paulo, were used to assess two protocols of indirect immunofluorescence assay (IFA) for leishmaniasis: one using a Leishmania major heterologous antigen (IFA-BM) and another using a Leishmania chagasi homologous antigen (IFA-CH). Two-graph receiver operating characteristic (TG-ROC) analysis was used to estimate accuracy. TG-ROC analysis compared 1:20 dilution readings of the homologous antigen (IFA-CH), considered as reference test, with IFA-BM dilutions (heterologous antigen).


RESULTS
The 1:20 dilution used in the IFA-CH test showed the best contingency coefficient (0.755) and the highest strength of association between the two variables studied (chi-square=124.3). Thus, it was considered the test reference dilution in comparisons with different IFA-BM test dilutions. The best IFA-BM results were obtained from 1:40 dilutions with the best contingency coefficient (0.680) and highest strength of association (chi-square=80.8). With the change in the cut-off point, recommended for the IFA-BM 1:40 dilution in this analysis, the specificity parameter value rose from 57.5% to 97.7%, even though the 1:80 dilution showed the best sensitivity estimate (80.2%), with the new cut-off point.


CONCLUSIONS
TG-ROC analysis can provide important information about diagnostic tests, in addition to offering suggestions on cut-off points that can improve test sensitivity and specificity estimates and assessing these tests in terms of the best cost-benefit ratio.
Seção de Parasitologia, Divisão de Laboratórios Regionais, Instituto Adolfo Lutz-Rio Claro, Rua Dez 152, Rio Claro, SP, Brazil. ritsilva@terra.com.br
Rita Maria da
RM
Silva
Márcia Dalastra
MD
Laurenti
Almério de Castro
Ade C
Gomes
Yeda Lopes
YL
Nogueira
D000818:Animals; D000953:Antigens, Protozoan / Q000276:immunology; D016009:Chi-Square Distribution; D004285:Dogs; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect / Q000379:methods*; D007201:Indicator Dilution Techniques; D018320:Leishmania major / Q000276:immunology; D007898:Leishmaniasis, Visceral / Q000097:blood / Q000175:diagnosis* / Q000662:veterinary; D008297:Male; D012680:Sensitivity and Specificity
D000953:Antigens, Protozoan