Version 3: Detection and significance of anti-Mycobacterium tuberculosis specific IgG antibody response for the diagnosis of pulmonary tuberculosis using enzyme-linked immunosorbent assay

Objective: Evaluation of an ELISA test for detection of IgG antibody response using in-house prepared Mycobacterium tuberculosis H37Rv soluble extract (MTSE) as antigen for rapid diagnosis of pulmonary tuberculosis and its clinical usefulness. 

Methods: In this study, a total of 758 pulmonary tuberculosis (TB) patients (652 AFB-positive and 106 AFB-negative), 276 healthy controls, and 43 pulmonary infectious disease controls other than TB were recruited. IgG antibody level against MTB soluble extract was measured in sera samples of all study groups using an ELISA test. The level of IgG antibody responses was compared among groups by the Kruskal-Wallis test. The pairwise comparison was made by the Mann-Whitney test, A positive score was represented by optical density above the cut–off value which was calculated from OD values of healthy controls by adding 2SD 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 healthy control and non-TB other pulmonary infectious disease control groups (p value<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% CI; 83.48-88.53), and the specificity was 96.74% (95% CI; 93.90-98.50). 

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