Tuberculosis

Laboratory investigations

Mantoux test

0.1 ml of 1:1,000 purified protein derivative (PPD) injected intradermally
Diameter of area measured 2-3 days later
Diameter Interpretation
<6mm Negative Not exposed
6-15mm Positive Suggests infection or previous BCG
>15mm Strongly positive Suggests active infection

(NB false negatives in HIV, lymphoma, age <6 months, sarcoidosis

Interferon gamma assays

Recommended if Mantoux is positive, and can discriminate positive Mantoux due to BCG from latent TB.

Management

Isoniazid
Rifampicin
Pyrazinamide
Ethambutol

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