Tuberculosis is diagnosed definitively by identifying the causative organism (''Mycobacterium tuberculosis'') in a clinical sample (for example, sputum or pus). When this is not possible, a probable diagnosis may be made using imaging (X-rays or scans) and/or a tuberculin skin test (Mantoux test).
The main problem with tuberculosis diagnosis is the difficulty in culturing this slow-growing organism in the laboratory (it may take 4 to 12 weeks for blood or sputum culture).
A complete medical evaluation for TB must include a medical history, a physical examination, a chest X-ray, microbiological smears, and cultures. It may also include a tuberculin skin test, a serological test.
The interpretation of the tuberculin skin test depends upon the person's risk factors for infection and progression to TB disease, such as exposure to other cases of TB or immunosuppression.
Tuberculin tests have the disadvantage in that they may produce false negatives, especially when the patient is co-morbid with sarcoidosis, Hodgkins lymphoma, malnutrition, or most notably active tuberculosis disease.
These are not affected by immunization or environmental mycobacteria, so generate fewer false positive results. The development of a rapid and inexpensive diagnostic test would be particularly valuable in the developing world.
Further Reading
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