ABSTRACT
Tuberculosis (TB) remains the leading single microbial illness globally, with one-third of the world's population infected with Mycobacterium tuberculosis. Pulmonary tuberculosis is the most common of all forms of TB and accounts for 70% of all cases. In Nigeria, pulmonary tuberculosis is diagnosed by the sputum smear microscopy after staining by Zehl-Neelsen method. The problems associated with the diagnosis of TB using smear and culture techniques have necessitated the exploration of the utility of serodiagnosis to support clinical suspicion of TB. Anti- M. tuberculosis IgG antibodies may aid in the diagnosis of active M. tuberculosis disease. The aim of the study was to test the diagnostic utility of the specific IgG serological assays for the diagnosis of pulmonary TB. It was studied whether anti-M. tuberculosisIgG antibodies are elevated in active M. tuberculosis disease. A diagnostic utility test of 184 participants in which 92 were smear positive pulmonary tuberculosis cases and 92 were apparently healthy controlswas conducted at the National Tuberculosis and Leprosy Training Centre Saye and the Ahmadu Bello University Teaching Hospital, Zaria, Kaduna. All samples were tested with theanti- M. tuberculosis IgG antibody assay. Of 92 patients with a positive sputum smear microscopy test, 17 (18.5%) were positive for M. tuberculosis antibodies. Eleven of the 92 (11.9%) controls were positive for M. tuberculosis antibodies. The sensitivity of IgG ELISA tests was 18% and the specificity was 90%, while the positive and negative predictive values were 66% and 53% respectively. Although anti- M. tuberculosis antibodies can be detected in patients with active M. tuberculosis disease, its detection may not be useful as an ideal adjunctive diagnostic.