Immunodiagnosis of tuberculosis: An update

Tuberculosis is still a major health problem in most developing countries and its incidence is rising in many developed countries. This resurgence has been attributed to the HIV epidemic and TB has been declared as a global health emergency by WHO in 1993. The diagnosis of tuberculosis mainly depends upon initial clinical suspicion and radiographic findings with subsequent bacteriological confirmation by sputum smear examination and culture. Lack of sensitivity in smear examination, non specificity of radiological findings, extended tum around time ofMycobacterium tuberculosis culture and difficulties in diagnosing paucibacillary, childhood and extrapulmonary tuberculosis has necessitated to explore the utility of immunodiagnosis of tuberculosis as a convenient and cost effective test to supplement clinical information for definite diagnosis. Many commercial tests are available in the market for diagnosis of TB. Most of these tests are based on the detection of IgG, IgA and IgM antibodies to specific mycobacterial antigen or mixture of antigens. Indigenous immunoassay systems have explored excretory-secretory ES-31 mycobacterial antigen for immunodiagnosis of TB. Many a time there is lack of consistent elevation in all the three Ig classes in active infection thus making it more important to determine the ideal antibody isotype assay for reliable diagnosis of tuberculosis and to save the costs of the patient for unnecessary investigations.