Standardization and evaluation of ELISA for the serodiagnosis of amoebic liver abscess

An ELISA test for the serological diagnosis of amoebic liver abscess (ALA) was standardized and evaluated in sera from three groups of patients: (1) three patients with diagnosis confirmed by isolation of the parasite, (2) thirty seven patients with diagnosis established by clinical findings and ultrasound studies and (3) seven patients whose diagnosis were established by clinical findings and a positive double immunodifusion test. Ninety one serum samples from healthy subjects and 22 from patients with other liver or parasitic diseases were also included in the study. The optimum concentration of Entamoeba histolytica antigen was 1.25 micrograms/ml and optimum dilutions of serum and anti-human IgG -alkaline phosphatase conjugate were 1:400 and 1:4000 respectively. The cut-off point of the ELISA test in this study was an absorbance value of 0.34. The test parameters were: sensitivity = 95.7%, specificity = 100%, positive predictive value = 100% and negative predictive value = 98.2%. The ELISA test was found to be of great use as a diagnostic tool for the establishment of amoebic etiology in patients with clinical supposition of ALA. The test could also be used for seroepidemiological surveys of the prevalence of invasive amoebiasis in a given population, since it allows the processing of a greater number of samples at a lower cost than other serological tests.