PP1 HOW MANY ABNORMAL CXR FINDINGS IN LTBI ARE OVERINTERPRETED? THE ROLE OF CT IN LTBI SCREENING

¹Dr Sharimini a/p Mani, ¹Dr Zamzurina Abu Bakar

Institut Perubatan Respiratori, Kuala Lumpur, Malaysia

Introduction
Chest radiograph is often employed as an initial LTBI (Latent TB infection) screening tool as per WHO 2018 guideline [1], especially in resource-limited settings. However, CXR has limitations due to its low specificity, leading to frequent overinterpretation of findings suggestive of tuberculosis [2]. Chest CT offers greater accuracy but involves higher cost and radiation exposure [3]. This study aimed to evaluate the utility of CXR in detecting active tuberculosis within MDR-TB contact cluster.

Objectives
To compare chest X-ray and CT findings in detecting active tuberculosis during LTBI screening.

Methodology
This retrospective study involved 39 asymptomatic individuals screened for LTBI. Those with positive IGRA testing underwent CXR, and those with abnormal radiographic findings (n=17) were scheduled for chest CT. The diagnostic concordance between CXR and CT findings were analysed.

Results
Among those screened for LTBI, 17 (43.6%) had abnormal CXR findings. Of these, 11 underwent chest CT, 4 showed active TB changes, while 7 had no active TB changes on chest CT suggesting likelihood of CXR overinterpretation with potential false positive rate of 63.6%. Factors contributing includes technical limitations (suboptimal penetration, poor inspiratory films), old PTB changes, and interobserver variability in interpretation. Among those with active TB changes on CT, predominant findings were centrilobular nodules with tree in bud opacities over the upper lobes (n=3). TB treatment was initiated in all patients with CT-confirmed active TB changes. Limitations of this study includes small sample size and potential bias from incomplete CT-follow up.

Conclusion
This study highlights the potential overinterpretation of CXR findings in LTBI screening and supports the utility of chest CT in confirming active TB changes.