Infectious Diseases >> Tuberculosis

Diagnosis

Early diagnosis of tuberculosis is important both to individuals and to community, and is very crucial yet difficult to achieve. Presently the diagnosis of tuberculosis largely depends upon clinical, radiological, cytological & bacteriological examinations.

• A chest X-ray is essential in all cases of suspected pulmonary tuberculosis. The classical X-ray picture of post-primary tuberculosis is of bilateral, posterior apical, cavitating, caseous lesions.
• Tuberculin skin test. A small amount of protein derived from mycobacteria is injected into the skin on the arm, and the area is examined after a day or two. A slightly raised, hard, red patch of skin at the site indicates the presence of TB (although not necessarily active disease). However, a positive TB skin test may also result from prior immunization with BCG. (John Hopkins Medicine)
• Sputum smears and culture. Examining sputum for TB bacteria is essential. The smear shows if TB-like organisms are present; smears are negative, however, in many patients who have TB, and some positive smears may be caused by organisms other than TB. The results of the culture may take three to six weeks to develop. A positive culture confirms diagnosis. (John Hopkins Medicine)
• Immunodiagnosis: SEVA TB ELISA (IgG & Ag) system based on the detection of tubercular IgG antibodies and antigen in tuberculosis has been developed and explored in several ways at this institute. The detection of IgG antibody (titre 1:600 and above) by indirect ELISA against SEVA TB ES 31/41 antigen in pulmonary and extra pulmonary tuberculosis suggests active tuberculosis infection. Free tubercular & Immune complexed antigen (IC-AG) is detected using affinity-purified anti ES-31 antibody by sandwich ELISA. A serum with an antigen titre of 1:300 and above is considered for positive reaction. The combination of antibody, free and IC-Ag detects 100% cases of pulmonary TB. The test is quite helpful in childhood tuberculosis where it is difficult to obtain sputum sample. This test has been found useful in clinically suspected and anti tuberculosis therapy (ATT) responded cases, which were negative for bacterial examination. This test has also been useful in confirming tubercular aetiology in extra-pulmonary tuberculosis (bone & joint, abdominal, CNS-meninges, lymph node, genito-urinary etc.)