IgM and IgG Antibodies in Tuberculosis
Introduction: The diagnosis of tuberculosis relies on the identification of acid-fast bacilli on unprocessed sputum smears using conventional light microscopy. Microscopy has high specificity in tuberculosis-endemic countries, but modest sensitivity which varies among laboratories (range 20% to 80%). Moreover, the sensitivity is poor for paucibacillary disease (e.g., pediatric and HIVassociated tuberculosis). Many supportive investigations including serolological tests being utilized for tuberculosis diagnosis have wide variations in sensitivity, specificity in different studies. The aim of study was to evaluate the recombinant 38 KDa antigen from M. tuberculosis - based Enzyme Immunoassays (EIA) test for its sensitivity, specificity and other statistical parameters.
Methods: This hospital based prospective cross-sectional study was conducted at Tribhuvan University Teaching Hospital, Kathmandu, from April 28, 2009 to November 30,2009. Sera from total 90 patients, pulmonary tuberculosis, extrapulmonary tuberculosis and non-tubercular chest infection patients who did not have past TB or exposure history , 30 in each group were used for Pathozyme Myco kit evalution to determine the IgM and IgG antibodies activity against the recombinant 38 KDa antigen of Mycobacteria
Results: In overall tuberculosis, IgM TB had sensitivity 48.3%,specificity 76.7%, positive predictive value 80.6% which was statistically significant(p=0.025) . The IgG TB had sensitivity 66.7%,specificity 83.3%,positive predictive value 88.9% which is statistically highly significant(p<0.001) to diagnose tuberculosis. Utilizing IgM and IgG both together, sensitivity decreased to 44.3%, but specificity increased to 90.0% and positive predictive value 88.5%, which was statistically significant (p=0.006) for the diagnosis of tuberculosis.
Conclusions: IgG TB antibody has high sensitivity and specificity for tuberculosis diagnosis, but IgM antibody should also be evaluated along with IgG antibody to increase specificity.
Keywords: Extrapulmonary tuberculosis (EPTB), 38 kDa antigen, IgM, IgG TB antibody, Pathozyme-Myco, Pulmonary tuberculosis (PTB).
Journal of Institute of Medicine, December, 2009; 31(3) 34-40