Elisa kit evaluation for IGG and IGM antibodies to A-60 tubercular protein antigen

Abstract

AIMS: The purpose of this study is to evaluate the A-60 antigen-based enzyme-linked immuno sorbent assay (ELISA) test for its sensitivity, specificity, and other related statistical parameters. SETTINGS AND DESIGN: Sera from 114 healthy volunteers, 105 bacteriologically confirmed cases of pulmonary tuberculosis (PTB), 59 sera from family contacts of PTB, and 40 sera from cases of lung infections other than tuberculosis collected from September to December 2003 were used for the kit evaluation. METHODS AND MATERIALS: Enzyme-linked immuno sorbent assay test using tuberculosis A-60 antigen-based kit manufactured by Anda Biologicals, France was used for the evaluation. STATISTICAL ANALYSIS: Differences in the optical density (OD) values for immunoglobulins G (IgG), and immunoglobulins M (IgM) antibodies in various groups were studied using t-test. RESULTS: On the basis of the findings the threshold value was setup as 400 U for IgG and mean OD for sera from healthy volunteers +2SD as the threshold for IgM. The sensitivity was 80% and specificity 95.8% for the IgG antibody test. The efficiency and predictive values were also high. The sensitivity for IgM was low (28.5%) but the specificity was high (95.7%). None of the 40 nontubercular lung infection cases were positive for the IgG and IgM antibody test for A-60, whereas five and three cases of 59 family contacts of PTB were positive for IgG and IgM antibody test. The test reproducibility was good for both IgG and IgM. CONCLUSION: IgG antibody test using A-60 antigen has good sensitivity and specificity, whereas IgM antibody test had high specificity but low sensitivity. Multicentric trials suggested evaluation of the diagnostic utility of the test for the extra-PTB.