The challenge of discordant serology in Chagas disease: The role of two confirmatory techniques in inconclusive cases

Abstract Serodiscordance in Chagas disease (CD) remains a challenge since individuals with inconclusive results are clinically complicated to manage. This work, conducted outside the endemic area, aims to compare two different confirmatory techniques for the diagnosis of CD in individuals without a definitive diagnosis, to analyze the performance of the screening techniques in this group of patients, and to describe the serological follow-up of these subjects over time. Sera from 48 individuals with repeatedly discordant results by one recombinant enzyme immunoassay (r-ELISA) and one native ELISA (n-ELISA), were included in the study. Confirmatory procedures were performed through TESA-blot, using trypomastigote antigens of Trypanosoma cruzi , and in-house WB (IH-WB) using a lysate from T. cruzi epimastigotes. Of the 48 sera, TESA-blot confirmed 22 (45.8%) cases and IH-WB 17 (35.4%). Both techniques showed a substantial agreement (k = 0.604). Confirmation defined as the positivity of one of the ELISA and at least one of the confirmatory tests was reached in 24/48 (50%) cases. We found a great dispersion of r-ELISA index values, especially among individuals with confirmatory negative results, ranging from 0.03–6.2. Additionally, n-ELISA yielded a better performance than r-ELISA in this cohort of patients, showing a significantly greater agreement with the confirmatory methods. Our results indicate that either confirmatory test could be an efficient tool to solve inconclusive cases regardless of which form of the parasite's life cycle they use. Also, most individuals remain with discordant serology throughout the short-term follow-up period time of study. Finally, we consider that it is necessary to establish a reference test feasible and commercialized in all areas to solve the problem of inconclusive results.