Evaluation of polymerase chain reaction for rapid diagnosis of clinically suspected tuberculous pleurisy

Evaluation of droplet digital PCR by detecting cell-free DNA in pleural effusion for the diagnosis of tuberculous pleurisy: a multicenter 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.

Challenges in pleural tuberculosis diagnosis: existing reference standards and nucleic acid tests

Pleural tuberculosis (pTB) is a grave form of extrapulmonary tuberculosis. Microbiological tests are usually found to be inadequate for pTB diagnosis. The absence of a uniform 'composite reference standard' is challenging; therefore, diagnosis is usually performed using a combination of diversified criteria. Nucleic acid tests vary in diagnostic accuracy and have not yet been integrated into clinical decision making. This review assesses the varied criteria used for pTB classification and the challenges afflicting pleural fluid-based DNA diagnostic tests, namely, PCR and Xpert^® MTB/RIF. In the 58 studies (PCR: n = 33; Xpert: n = 25) analyzed, reference standards were heterogeneous and PCR/Xpert pooled sensitivity values (range: 0-100%) were inadequate. However, the consistent high specificity of Xpert (range: 90-100%) indicated its utility as a 'rule-in' test. There is an urgent need to evaluate existing and new molecular tests in well-designed studies  to accurately assess their utility for pTB diagnosis. To conclude, rapid and accurate tests are warranted for pTB diagnosis.

Evaluation of nested polymerase chain reaction for rapid diagnosis of clinically suspected tuberculous pleurisy

BACKGROUND

Early diagnosis of tuberculosis is important in its control. The conventional techniques like smear microscopy and culture suffer from low sensitivity for diagnosis of extra-pulmonary tuberculosis like Pleural Tuberculosis (PTB) due to paucibacillary nature of the fluid. Polymerase Chain Reaction (PCR) is presently seen as a promising alternative to conventional techniques. In this study we have evaluated IS6110 sequence based nested PCR (nPCR) for the detection of Mycobacterium tuberculosis (MTB) DNA directly from clinical samples. The results of PCR were compared with the results of conventional methods like smear, culture and Adenosine Deaminase (ADA) activity.

MATERIAL AND METHODS

A total of 50 pleural fluid samples from the patients with history suggestive of tuberculosis were taken. All the samples were processed for Ziehl-Neelsan (ZN) staining for Acid Fast Bacilli (AFB), culture ADA activity and PCR with primers targeting 123bp fragment of IS6110 of MTB complex.

RESULTS

A significant difference was seen in the sensitivities of conventional methods and PCR (p<0.05). Out of these 50 samples 3 were positive by smear, culture was positive in 5 samples, 21 samples showed high ADA activity and 29 were positive by PCR with overall 100% sensitivity of PCR using culture on LJ media as gold standard.

CONCLUSIONS

The combined analysis of nPCR, ADA activity and other lab investigations can be very useful in the rapid diagnosis in cases of PTB.

Improved diagnosis of central nervous system tuberculosis by MPB64-Target PCR

Central nervous system (CNS) tuberculosis is a serious clinical problem, the treatment of which is sometimes hampered by delayed diagnosis. Clearly, prompt laboratory diagnosis is of vital importance as the spectrum of disease is wide and abnormalities of the cerebrospinal fluid (CSF) are incredibly variable. Since delayed hypersensitivity is the underlying immune response, bacterial load is very low. The conventional bacteriological methods rarely detect Mycobacterium tuberculosis in CSF and are of limited use in diagnosis of tuberculous meningitis (TBM). This double blind study was, therefore, directed to the molecular analysis of CNS tuberculosis by an in-house-developed PCR targeted for amplification of a 240bp nucleotide sequence coding for MPB64 protein specific for Mycobacterium tuberculosis. Based on the clinical criteria, 47 patients with CNS tuberculosis and a control group of 10 patients having non-tubercular lesions of the CNS were included in the study. Analyses were done in three groups; one group consisting of 27 patients of TBM, a second group of 20 patients with intracranial tuberculomas and a third group of 10 patients having nontubercular lesions of the CNS acted as control. There were no false positive results by PCR and the specificity worked out to be 100%. In the three study groups, routine CSF analysis (cells and chemistry), CSF for AFB smear and culture were negative in all cases. PCR was positive for 21/27 patients (77.7% sensitivity) of the first group of TBM patients, 6/20 patients (30% sensitivity) of the second group with intracranial tuberculomas were positive by PCR and none was PCR-positive (100% specificity) in the third group. Thus, PCR was found to be more sensitive than any other conventional method in the diagnosis of clinically suspected tubercular meningitis.