Will latent tuberculosis (TB) be visible on a chest X-ray, or do abnormal TB findings on an X-ray indicate active tuberculosis at some point?

From the Guidelines

Latent TB typically does not show up on a chest X-ray, and if TB findings are visible on an X-ray, this usually indicates that the person has had active TB at some point, either currently or in the past. The diagnosis of latent TB relies primarily on tuberculin skin tests (TST) or interferon-gamma release assays (IGRAs) like QuantiFERON-TB Gold or T-SPOT.TB test, not X-rays 1. When X-rays do show TB-related abnormalities such as infiltrates, nodules, cavities, or fibrotic scars, these findings suggest that TB was active at some point, though they cannot definitively determine if the infection is currently active without additional testing 2.

Key Considerations

• Chest radiography has high sensitivity for detecting manifestations of active TB, but relatively poor specificity due to overlap with nontuberculous pulmonary infection 1.
• 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 1.
• CT may be helpful in cases where chest radiography does not show "classic" findings of TB, and can better show distinct findings such as cavitation or endobronchial spread with tree-in-bud nodules 2.

Diagnostic Approach

• Chest radiography is usually the first study performed in patients suspected of having TB, and can reveal ancillary findings of TB such as pleural effusion or spondylitis 3.
• To distinguish between old healed TB and current active disease, doctors consider clinical symptoms (fever, cough, weight loss), sputum tests for TB bacteria, and sometimes compare with previous X-rays to check for changes over time 2.
• The distinction between active and latent TB is important because active TB requires a full treatment regimen, while latent TB may be treated with a simpler preventive therapy.

From the Research

Latent Tuberculosis Visibility on Chest X-ray

• Latent tuberculosis (TB) may not be visible on a chest X-ray, as the disease can be in a dormant state and not produce any noticeable symptoms or radiological signs 4, 5.
• Abnormal TB findings on an X-ray do not necessarily indicate active tuberculosis, as they can also be suggestive of latent TB infection (LTBI) or past infection 6, 5.
• The diagnostic accuracy of chest radiography for latent TB infection is limited, and other tests such as the tuberculin skin test (TST) and interferon-gamma release assays (IGRA) are often used in combination with chest X-ray to diagnose LTBI 5, 7.

Differentiating Active TB from Latent TB

• High-resolution CT (HRCT) scanning of the chest can be helpful in differentiating active TB from LTBI, as it can detect lesions suggestive of active TB that may not be visible on a chest X-ray 6.
• CT scanning can also distinguish active from inactive disease, making it a useful tool in the diagnosis and management of TB 5, 8.
• The use of CT scanning in combination with other diagnostic tests can improve the diagnostic accuracy of TB and help identify individuals with latent TB infection who are at risk of developing active disease 6, 5, 8.