Detection and Significance of Anti-Mycobacterium tuberculosis-specific Immunoglobulin G Antibody Response for the Diagnosis of Pulmonary Tuberculosis Using Enzyme-linked Immunosorbent Assay.

Background: This study evaluates an enzyme-linked immunosorbent assay test for the detection of immunoglobulin G (IgG) antibody response using in-house prepared Mycobacterium tuberculosis H37Rv soluble extract (MTSE) antigen for rapid diagnosis of pulmonary tuberculosis (PTB).

Methods: A total of 758 PTB patients (652 acid-fast bacilli [AFB] positive and 106 AFB-negative), 276 healthy controls, and 43 pulmonary infectious disease controls other than TB were recruited. IgG antibody level against MTSE was measured in serum samples of all study groups. The level of IgG antibody responses was compared among groups by the Kruskal-Wallis test, and pairwise comparison was made by the Mann-Whitney test. A positive score was represented by optical density (OD) above the cutoff value, which was calculated from OD values of healthy controls by adding 2 standard deviations (SDs) to the mean OD value. The evaluation of diagnostic value was considered based on sensitivity and specificity.

Results: Significantly higher levels of IgG antibody response were observed in PTB patients compared to other groups (P < 0.0001). The percent positivity for the IgG antibody response was higher in AFB-positive 574/652 (88.04%) and 79/106 (74.53%) AFB-negative PTB patients as compared to healthy control 9/276 (3.26%) and non-TB other pulmonary infectious disease control 3/43 (6.97%). The sensitivity of the test in PTB patients (AFB-positive and AFB-negative) was 86.15% (95% confidence interval [CI]: 83.48-88.53), and the specificity was 96.74% (95% CI: 93.90-98.50).

Conclusion: This immunological test could be an efficient test in detecting IgG antibody response in PTB patients and could be useful for diagnosing AFB-negative presumptive TB cases.