Serological Diagnosis of Chronic Chagas Disease: Is It Time for a Change?

Abstract

Chagas disease has spread to areas that are nonendemic for the disease with human migration. Since no single reference standard test is available, serological diagnosis of chronic Chagas disease requires at least two tests. New-generation techniques have significantly improved the accuracy of Chagas disease diagnosis by the use of a large mixture of recombinant antigens with different detection systems, such as chemiluminescence. The aim of the present study was to assess the overall accuracy of a new-generation kit, the Architect Chagas (cutoff, ≥1 sample relative light units/cutoff value [S/CO]), as a single technique for the diagnosis of chronic Chagas disease. The Architect Chagas showed a sensitivity of 100% (95% confidence interval [CI], 99.5 to 100%) and a specificity of 97.6% (95% CI, 95.2 to 99.9%). Five out of six false-positive serum samples were a consequence of cross-reactivity with Leishmania spp., and all of them achieved results of <5 S/CO. We propose the Architect Chagas as a single technique for screening in blood banks and for routine diagnosis in clinical laboratories. Only gray-zone and positive sera with a result of ≤6 S/CO would need to be confirmed by a second serological assay, thus avoiding false-positive sera and the problem of cross-reactivity with Leishmania species. The application of this proposal would result in important savings in the cost of Chagas disease diagnosis and therefore in the management and control of the disease.

FIG 1

Overall serum value distribution of ELISAc (A), ELISAr (B), and Architect Chagas (C). Serum samples from panel I (samples from chronic chagasic seropositive patients, n = 107), panel II (samples from nonchagasic patients, n = 125), panel III (samples with discrepant serological results, n = 12), and panel IV (samples from patients with other infections, n = 71) are represented. Filled circles (●) indicate true-positive and negative results, open circles (○) indicate false-positive and negative results, and Xs (×) represent results in the gray zone. Dashed lines represent the cutoff value established for each test: 20 units for ELISAc (A), 1 absorbance/cutoff value for ELISAr (B), and 1 relative light unit/cutoff value for Architect Chagas (C). The dotted line in panel C indicates the point of the 6 relative light units/cutoff value on the y axis.