Utility of plasma cell-free DNA detection using homobifunctional imidoesters using a microfluidic system for diagnosing active tuberculosis

Background It is difficult to diagnose tuberculosis (TB), particularly sputum-scarce pulmonary TB and extrapulmonary TB, using conventional diagnostic tests. Since these cases require additional invasive procedures to obtain appropriate specimens, new non-invasive diagnostic tests are needed. Plasma cell-free DNA (cfDNA) detection has gained interest as a novel diagnostic test for TB as it is convenient and less invasive. Therefore, we investigated the performance of enriched cfDNA for diagnosing pulmonary TB and extrapulmonary TB. Methods All patients suspected to have TB, who consented to the use of blood for detecting cfDNA, were prospectively enrolled from January 2019 to June 2020. We categorised the patients as confirmed, probable, possible TB, and not-TB. We compared the performance of cfDNA with those of conventional diagnostic tests. Results Among the 96 patients enrolled, 40 (41.7%) had TB, including 34 with confirmed TB and six probable TB, and 41 (42.7%) did not have TB. Acid-fast bacilli microscopy, Xpert MTB/RIF, and mycobacterial culture results were positive in 12 (31.6%), 22 (61.1%), and 25 (65.8%) patients, respectively. The sensitivity and specificity of cfDNA were 80.0% and 78.1%, respectively. While the sensitivity and specificity of cfDNA were similar to those of interferon-gamma releasing assay (IGRA) (sensitivity 80.6% and specificity 71.4%), the combined sensitivity and specificity of the two assays were 94.4% and 64.3%, respectively, which can be used to rule out TB. Conclusions Plasma cfDNA assay seems to be a useful adjunct to the current tests for diagnosing TB, especially when used in combination with IGRA for ruling out TB.