From the Guidelines
A chest x-ray (CXR) is used to help determine if a tuberculosis (TB) infection is active or latent, as it can reveal characteristic abnormalities such as infiltrates, cavities, or nodules in the lungs that suggest active TB disease. According to the American College of Radiology Appropriateness Criteria 1, chest radiography has high sensitivity for detecting manifestations of active TB, particularly in high-risk patients. The yield of chest radiography in high-risk patients ranges from 1% to 7%, although it is not clear how many of these cases would have been suspected on the basis of clinical symptoms alone.
Key Findings
- Chest radiography should be performed as the initial test to identify individuals with active TB 1.
- A CXR can reveal characteristic abnormalities such as infiltrates, cavities, or nodules in the lungs that suggest active TB disease, particularly in the upper lobes.
- Individuals with latent TB infection typically have normal chest x-rays because the bacteria are dormant and not causing active disease.
- However, a CXR alone is not sufficient for definitive diagnosis and should be used in conjunction with other diagnostic tools such as tuberculin skin tests, interferon-gamma release assays (IGRAs), and microbiological tests like sputum cultures or molecular tests for Mycobacterium tuberculosis.
Diagnostic Approach
- The World Health Organization recommends that chest radiography should be performed before latent TB infection treatment to rule out active TB disease 1.
- The U.S. Public Health Service and the Infectious Diseases Society of America also recommend that all HIV-infected persons who have a positive TST result should undergo chest radiography and clinical evaluation to rule out active TB 1.
- Some individuals with latent TB may have abnormal CXR findings from previous TB disease that has healed, which can appear as fibrotic scars or calcifications, and these findings must be interpreted in the context of the patient's clinical presentation, risk factors, and other test results to determine whether the infection is currently active or latent.
From the Research
Use of Chest X-ray in Determining Active or Latent TB Infection
- A chest x-ray (CXR) is used as a diagnostic tool to help determine if a tuberculosis (TB) infection is active or latent 2, 3, 4, 5, 6.
- The CXR has good sensitivity but poor specificity for the diagnosis of pulmonary TB, and radiographic diagnosis of active disease can only be reliably made on the basis of temporal evolution of pulmonary lesions 2.
- Computed tomography (CT) is considered a complementary imaging modality to CXR in the screening procedure to detect past and latent TB infection in specific subgroups of patients who have increased risk for TB reactivation 2.
- Studies have shown that CXR can identify findings suggestive of pulmonary TB in asymptomatic children with a positive tuberculin skin test and/or interferon-γ release assay (TST/IGRA) 3.
- A simple classification of TB-related chest radiographic abnormalities into five broad categories has moderate to substantial reproducibility of readings, with reasonable validity 4.
- Chest X-ray and bacteriology are valuable tools for the evaluation of pulmonary tuberculosis, and the extent of radiographic lesions correlates with bacteriological parameters 5.
- The performance of computer-aided detection digital chest X-ray reading technologies for triage of active TB among persons with a history of previous TB is decreased among those with previous TB 6.
Limitations and Considerations
- The use of CXR in determining active or latent TB infection has limitations, including poor specificity and the need for complementary imaging modalities such as CT 2.
- The performance of CXR and computer-aided detection technologies can be affected by the presence of sequelae in patients with previously treated TB 6.
- The diagnosis of active TB requires a combination of clinical evaluation, radiographic findings, and microbiological confirmation 3, 4, 5.