Evaluation of droplet digital polymerase chain reaction by detecting cell-free deoxyribonucleic acid in pleural effusion for the diagnosis of tuberculous pleurisy: a multicentre cohort study

Objectives Tuberculous pleurisy is one of the most common extra-pulmonary tuberculosis, but the sensitivity of conventional mycobacterial culture (Culture) or Xpert MTB/RIF assay (Xpert) is not satisfying. This multicenter cohort study evaluated the accuracy of a new cell-free DNA droplet digital PCR assay (cf-ddPCR) for diagnosing Tuberculous pleurisy. Methods Patients with suspected tuberculosis (≥ 5 years of age) with pleural effusion were consecutively recruited from nine research sites across six provinces in China between September 2020 to May 2022. Culture, Xpert, Xpert MTB/RIF Ultra assay (Ultra), real-time PCR and cf-ddPCR were performed simultaneously for all specimens. Results A total of 321 participants were enrolled, and data from 281 (87.5%) participants were available, including 105 definite Tuberculous pleurisy, 113 possible Tuberculous pleurisy and 63 non-Tuberculous pleurisy according to the composite reference standard. The sensitivity of cf-ddPCR was 90.5% (95/105, 95% CI = 82.8% to 95.1%) in the definite Tuberculous pleurisy group, which was significantly higher than those of Culture (57.1%, 60/105, 95% CI = 47.1% to 66.6%, P<0.001), Xpert (46.7%, 49/105, 95% CI = 37.0% to 56.6%, P<0.001), Ultra (69.5%, 73/105, 95% CI = 59.7% to 77.9%, P<0.001) and real-time PCR (75.2%, 79/105, 95% CI: 65.7% to 82.9%, P < 0.001). In possible Tuberculous pleurisy, whose results of Culture and Xpert were both negative, the sensitivity of cf-ddPCR was 61.1% (69/113, 95% CI = 51.4% to 70.0%), which was still significantly higher than that of Ultra (27.4%, 31/113, 95% CI = 19.7% to 36.8%, P<0.001) and real-time PCR (38.9%, 44/113, 95% CI: 30.0% to 48.6%, P < 0.001). Conclusions The performance of cf-ddPCR is superior to Culture, Xpert, Ultra and real-time PCR, indicating that improved diagnostic accuracy can be anticipated by incorporating this new assay.