Diagnostic accuracy of plasma cfdna (cell-free dna) in tuberculosis

Abstract

Background: Tuberculosis (TB) remains a significant global health burden, requiring rapid and accurate diagnostic methods. Conventional diagnostic techniques such as Ziehl Neelsen stained (ZN-stained) acid-fast bacilli (AFB) smear test has limitations in sensitivity and culture has long turnaround times, while Cartridge based nucleic acid amplification test (CBNAAT/GeneXpert) has variable sensitivity, especially in extrapulmonary tuberculosis (EPTB). This study evaluates the diagnostic accuracy of plasma cell-free DNA (cfDNA) in detecting Mycobacterium tuberculosis (MTB) and its correlation with ZN-stained AFB smear test and GeneXpert assay. Methods: A cross-sectional study was conducted on 94 clinically suspected TB patients. Plasma cfDNA was extracted and analyzed using quantitative PCR for the IS6110 gene (MTB). Results were compared with Ziehl-Neelsen stained AFB smear test and taking CBNAAT (GeneXpert) as reference standards. Diagnostic parameters such as sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and overall accuracy were assessed. Results: Plasma MTB-cfDNA testing showed a sensitivity of 93.3% and specificity of 95.3%, with a PPV of 90.3% and an NPV of 96.8%. The overall diagnostic accuracy was 94.68%. In comparison, ZN-stained AFB smear test showed lower sensitivity (53.3%) but high specificity (95.3%). Plasma cfDNA testing was particularly useful in smear-negative and EPTB cases, detecting TB in samples that were negative on GeneXpert assay. Conclusion: Plasma cfDNA is a highly specific and sensitive diagnostic tool for TB, offering a minimally invasive and rapid alternative to traditional diagnostics. Its ability to detect TB in smear-negative and EPTB cases makes it a valuable adjunct to CBNAAT/GeneXpert assay.