TB Screening Tools: Chest X-ray as a Triage Tool

Chest radiography or X-ray (CXR) can be used as an effective triage test for those seeking care for respiratory complaints. 

It is an effective triage tool in tuberculosis (TB) because:

1. ​It is a sensitive tool for identifying TB, i.e., it identifies most people with TB, while correctly ruling out TB in most persons, if negative.
2. It suggests further diagnostic evaluation patients may require to correctly diagnose the cause of their illness.
3. CXR may have higher specificity for pulmonary TB than assessing symptoms alone, depending on how the X-ray is read.
   • Triaging using CXR can help reduce the number of persons who undergo bacteriological TB testing without decreasing the detection of true TB cases.
4. CXR also improves the positive predictive value of subsequent bacteriological tests by increasing the pre-test probability of TB.
5. Beyond identifying active TB disease, CXR also identifies one of the populations at highest risk of developing TB disease: those who have inactive TB or fibrotic lesions without a history of TB treatment. Once active TB has been excluded, patients with fibrotic lesions should be followed-up, given their high risk for developing active disease.

It is important that any CXR abnormality consistent with TB be further evaluated with a bacteriological test (see figure below).

Figure: Using CXR as a TB Triage Tool; Source: Chest Radiography in Tuberculosis Detection, WHO, p.11

Resources

• Systematic Screening for Active Tuberculosis; Principles and Recommendations, WHO 2013.
• Chest Radiography in Tuberculosis Detection, End-TB Strategy, WHO, 2016.

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