title: Calculation of the ELISA's cut-off based on the change-point analysis method for detection of Trypanosoma cruzi infection in Bolivian dogs in the absence of controls.
abstract: In ELISAs, sera of individuals infected by Trypanosoma cruzi show absorbance values above a cut-off value. The cut-off is generally computed by means of formulas that need absorbance readings of negative (and sometimes positive) controls, which are included in the titer plates amongst the unknown samples. When no controls are available, other techniques should be employed such as change-point analysis. The method was applied to Bolivian dog sera processed by ELISA to diagnose T. cruzi infection. In each titer plate, the change-point analysis estimated a step point which correctly discriminated among known positive and known negative sera, unlike some of the six usual cut-off formulas tested. To analyse the ELISAs results, the change-point method was as good as the usual cut-off formula of the form "mean + 3 standard deviation of negative controls". Change-point analysis is therefore an efficient alternative method to analyse ELISA absorbance values when no controls are available.
authors.affiliation: Institut de Recherche pour le Développement, La Paz, Bolivia.|Instituto Nacional de Laboratorios de Salud, La Paz, Bolivia.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Lardeux
authors.affiliation: Institut de Recherche pour le Développement, La Paz, Bolivia.|Instituto Nacional de Laboratorios de Salud, La Paz, Bolivia.
authors.forename: Gino
authors.initials: G
authors.lastname: Torrico
authors.affiliation: Institut de Recherche pour le Développement, La Paz, Bolivia.|Instituto Nacional de Laboratorios de Salud, La Paz, Bolivia.
authors.forename: Claudia
authors.initials: C
authors.lastname: Aliaga
mesh_terms: D000818:Animals; D000913:Antibodies, Protozoan / Q000097:blood*; D001838:Bolivia; D014355:Chagas Disease / Q000175:diagnosis / Q000662:veterinary*; D004283:Dog Diseases / Q000175:diagnosis*; D004285:Dogs; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods / Q000662:veterinary*; D012016:Reference Values; D012680:Sensitivity and Specificity; D014349:Trypanosoma cruzi / Q000276:immunology*
chemical_list: D000913:Antibodies, Protozoan