Diagnosis of Tuberculosis

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Diagnosis of Tuberculosis in Adults and Children

Recommendations on TB testing incorporate recent evidence on using an interferon-gamma release assay for latent TB and nucleic acid amplification testing for active TB.

Target Population: Clinicians, laboratory workers, staff in medical offices, academic training programs, medical schools, and others involved in the management of patients with latent or suspected tuberculosis (TB)

Sponsoring Organizations: American Thoracic Society, Infectious Diseases Society of America, Centers for Disease Control and Prevention

Background and Objective

These evidence-based consensus guidelines were formulated using the Grading, Recommendations, Assessment, Development, and Evaluation (GRADE) approach.

Key Points

  • TB is a leading cause of infectious disease morbidity and mortality worldwide but, unfortunately, has many diagnostic uncertainties.

  • For testing an individual suspected of having latent TB infection, an interferon-gamma release assay (IGRA) is preferred over a tuberculin skin test (TST) except in people at high risk for progression (for whom either test is appropriate) and in children younger than 5 years. However, a TST is considered an acceptable alternative.

  • For diagnosis of suspected pulmonary TB, a sputum volume of at least 3 mL (optimally, 5–10 mL) is required. Sputum induction rather than flexible bronchoscopic sampling is suggested for individuals unable to expectorate sputum or whose expectorated sputum is acid-fast bacilli (AFB) smear microscopy negative, leaving bronchoscopy for those unable to provide induced sputum.

  • Three specimens from each patient with suspected TB should be examined microscopically for AFB. Both liquid and solid mycobacterial cultures should be performed for every specimen, and recovered isolates should be identified according to standard criteria.

  • A nucleic acid amplification test (NAAT) is recommended in AFB-positive patients and in AFB-negative patients with high suspicion of pulmonary TB.

  • Rapid molecular drug susceptibility testing for rifampin and, optionally, for isoniazid is recommended in AFB-positive or patients with a positive NAAT who are at risk for drug-resistant tuberculosis.

  • For suspected extrapulmonary TB, the diagnostic approach is similar to that for pulmonary TB. Patients with suspected pleural, peritoneal, pericardial, or central nervous system TB also should have adenosine deaminase and/or free IFN-γ levels determined in liquid specimens; in addition, tissue biopsies should be examined histologically.

  • From each patient with confirmed TB, an isolate should be genotyped for epidemiological reasons.

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