Discriminatory Power and Concordance between ELISA-F29 and PCR in Individuals with Infection due to T.cruzi

Abstract

Introduction: The diagnosis of infection with Trypanosoma cruzi (T. cruzi) is routinely performed by serological tests while the use of molecular methods is still in process of standardization.  Objective: To evaluate the discriminatory capacity and agreement between a serological test and a polymerase chain reaction (PCR) to determine T. cruzi infection. Methodology: PCR and ELISA test-F29 were performed to 95 participants of “Cardiovascular health investigation and collaboration countries of America to assess the markers and outcomes of Chagas disease” (CHICAMOCHA). Discriminatory capacity of ELISA –F29 with respect to PCR results were evaluated by estimating the area of ROC curve.  The false positive rate was estimated to 25% and sensitivity to 75%. The agreement was determined using Cohen's kappa. Results: PCR tests were performed at two different times in 95 individuals (mean age: 38; 64% male), with positivity rates between 1.1 to 2.2% for S35-S36 primers and from 18.3% to 34, 7% for primers 121-122, respectively. ELISA-F29 discriminatory capacity regarding PCR was 0.62 (95% CI: 0.53, 0.70). The false positive rate was 56% (95% CI: 42; 70). The optimal cutoff for absorbance ratio of ELISA-F29 was 2.53 (sensitivity 59%, specificity 60%). For the primers 121-122, levels of observed agreement and kappa estimates were 52.6% and 0.10 (95% CI: -0.08, 0.28) for the first measurement, 62.4% and 0.09 (95% CI: -0.09, 0.28) for the second measurement, and 57.5% and 0.13 (95% CI: 0.01, 0.26) for the two measurements simultaneously evaluated. Conclusions: The results show poor agreement evidenced by kappa values determined in the study. It is necessary to refine the studies to evaluate the utility of molecular testing in the diagnosis of Chagas disease.[Gómez-Laitón ED, Polo-Ardila LA, Castellanos-Domínguez YZ, Herrera VM, Villar JC. Discriminatory power and concordance between ELISA-F29 and PCR in individuals with infection due to T.cruzi. MedUNAB 2015; 18 (1): 27-33].