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MCQs in Tropical Medicine

Rob Skelly DTM+H FRCP

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Answer 25

Concerning tuberculin skin testing

True a. patients with tuberculous pericarditis are usually tuberculin positive
False b. previous BCG vaccination usually results in a strongly positive reaction
True c. pulmonary sarcoidosis gives a positive tuberculin test in about 30% of cases
False d. if the sputum microscopy and culture are negative for mycobacteria, pulmonary tuberculosis can only be diagnosed if the tuberculin test is positive.
True e. the test is usually negative in miliary tuberculosis

Young children, the elderly and the immunosuppressed may fail to mount an adequate immune response. They are often tuberculin negative in the presence of active disease. In such cases the patients often become tuberculin positive during treatment.

BCG vaccination usually results in a positive tuberculin test. Sometimes the tuberculin test remains negative. A strongly positive tuberculin test should always raise the possibility of active tuberculosis.

Sputum negative, tuberculin negative pulmonary tuberculosis is being increasingly diagnosed. The patient may be HIV positive. The diagnosis is based on clinical features, exposure history and chest radiograph appearance and may need to be re-considered in the response to treatment is poor.

Characteristically in sarcoidosis the patient is tuberculin negative and Kveim positive.
However, upto 30% will be tuberculin positive and upto 30% Kveim negative.

Copyright: Rob Skelly 2006