How Is Tuberculosis Diagnosed?
Those at risk for new TB infection:
- Close and even casual contact with untreated persons with active TB
- Illicit drug use
- Those in institutionalized settings
- Health workers
Those at risk for reactivation:
- HIV infection
- Immunocompromise (transplant, chemotherapy, etc.)
- Renal failure (dialysis)
- Those on systemic steroids
- Those from TB-endemic countries
A tuberculin skin test should be performed in any person with a cough lasting for weeks, accompanied by lymph node enlargement, fever, and weight loss. A positive test only indicates exposure and possibly active infection. This test is useful for identifying latent TB.
TB diagnosis is established by isolating M. tuberculosis from bodily secretions such as sputum, bronchial lavage, pleural fluid, or tissue (lung/pleural biopsy). Another test is to test for acid-fast (stain) bacteria and nucleic acid amplification. X-rays are supportive tools only.
Tests for drug-resistant TB are necessary when there has been prior TB treatment or progression while on TB medication. Culture of the Mycobacterium with sensitivity testing for anti-TB drugs will identify any drug-resistances.
Bronchoscopy can be done when other attempts to retrieve material for culture fail. When this is not definitive, tissue biopsy is the next step.