Plasma MTB cfDNA Before Bronchoscopy

Tuberculosis (TB) remains a major global health challenge, affecting over 10 million people annually. Hong Kong carries an intermediate TB burden, with \~3,200 new cases reported yearly. Pulmonary TB (PTB), the most common form, presents diagnostic difficulties. Traditional methods like sputum smear and culture often fail in patients unable to produce adequate samples, necessitating bronchoscopy to collect bronchoalveolar lavage (BAL) for mycobacterial testing.

These limitations pose risks for patients and strain healthcare systems. Bronchoscopy is invasive, resource-intensive, and may delay treatment-especially for elderly patients with comorbidities. Blood-based inflammatory markers lack diagnostic specificity. A rapid, non-invasive alternative is urgently needed.

The investigators developed a plasma-based assay that detects Mycobacterium tuberculosis cell-free DNA (MTB cfDNA) in blood. This liquid biopsy leverages metagenomic sequencing and computational analysis to identify TB-specific genetic material while minimizing contamination. Preliminary data show excellent diagnostic performance, with area under the receiver operating characteristic curve values \>0.94 for TB pleurisy.

The investigators propose a prospective clinical validation study comparing plasma MTB cfDNA testing to bronchoscopy with BAL culture and molecular testing. The primary aim is to demonstrate non-inferiority of plasma cfDNA within a 10% sensitivity margin. Secondary aims include assessing how clinical and radiological features affect test performance and evaluating the assay's ability to detect drug resistance mutations for personalized therapy.

Validation could transform TB diagnosis by offering a rapid, safe, and accurate blood test. Patients could avoid invasive procedures, receive faster diagnoses, and begin treatment sooner. Detecting resistance mutations directly from plasma would enable timely, targeted therapy-critical for addressing multidrug-resistant TB. This represents a paradigm shift toward precision medicine in TB care.

Tailored to Hong Kong's epidemiological context, this study addresses a key diagnostic gap. The approach has global relevance, with potential to improve clinical outcomes, reduce costs, and accelerate progress toward WHO's TB elimination goals.