Detection of Mycobacterium tuberculosis Antigens in Sputum for the Diagnosis of Pulmonary Tuberculosis

ABSTRACT

As an effort to develop a rapid and sensitive diagnostic test, we produced previously a monoclonal antibody (MAb) specific to the lipoarabinomannan (LAM) antigen and used in a sandwich ELISA for detection of mycobacterial antigens in sputum. In this study, we attempted to improve the antigen detection assay by combination of af5nity-purified antibodies against Mycobacterium tuberculosis soluble antigen and anti-LAM MAb. With the new assay, the LAM antigen was detectable as low as 2 ng/ml, and none of 10 gram-negative and gram-positive organisms gave significant absorbance, thus indicating the specific detection of mycobacterial antigens. Sputum samples from 62 patients who were suspected having tuberculosis and from 37 healthy controls were examined. The sensitivity of the antigen detection assay ranged from 0% in the 1+ culture group to 78.8% in the 3+ culture group. When the results were combined, 15 of 24 culture-positive samples were antigen-positive, thus giving an overall sensitivity of 62.5%. The overall specificity was 96.0%, when all the culture-negative samples were combined. The results thus demonstrate that the antigen detection assay can provide a rapid supplemental information for the diagnosis of pulmonary diagnosis.