Purpose: There is a need for a continued effort to develop rapid immunodiagnostic assays for tuberculosis (TB) infection with greater sensitivity and specificity that can be used in the field and in the laboratory and that can be formatted for use with multiple species. This would help to obtain definitive early diagnosis of TB. The present study was developed to determine the role of using early secreted antigenic target-6 (ESAT-6) in immunodiagnosis of Mycobacterium tuberculosis. Methods: Serum samples were obtained from TB infected patients and normal healthy controls. Two rapid immunodiagnostic assays (Enzyme-linked immunosorbent assay (ELISA) and Immunoblotting) were performed. Results: The sensitivity of immunoblotting assay was 100%;however, ESAT-6 antigen was not able to discriminate between patients and normal controls. Application of direct ELISA using ESAT-6 antigen yielded 97.6% sensitivity and 75% specificity for the diagnosis of TB infection. Conclusion: In conclusion, the detection of antibodies against ESAT-6 antigen in the sera of TB patients by direct ELISA could be used as a preliminary assay for diagnosis of human M. tuberculosis infection. A combination of the ELISA with either radiological or microscopic examination is required to overcome the low specificity of the assay for negative results.
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