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Review 2: "Accuracy of Lung and Abdominal Ultrasound for Tuberculosis Diagnosis: A Prospective Cohort Study from India"

Reviewers believe that the study highlights the potential and current limitations of POCUS in diagnosing TB, making it not suitable to be a standalone test for the time being.

Published onJul 31, 2024
Review 2: "Accuracy of Lung and Abdominal Ultrasound for Tuberculosis Diagnosis: A Prospective Cohort Study from India"
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key-enterThis Pub is a Review of
Accuracy of lung and abdominal ultrasound for tuberculosis diagnosis: a prospective cohort study from India
Accuracy of lung and abdominal ultrasound for tuberculosis diagnosis: a prospective cohort study from India
Description

Abstract Background Point-of care ultrasound is considered to hold promise in tuberculosis (TB) screening. However, most available abdominal ultrasound data focuses on HIV-infected cohorts and for lung ultrasound (LUS) data is very sparse. We aimed to determine accuracy of lung and abdominal ultrasound in a cohort of presumed TB in a tertiary care hospital in India.Methods Adult patients with presumed TB were enrolled prospectively and underwent a comprehensive ultrasound evaluation. Accuracy of individual and a predetermined combination of findings was determined against a TB reference standard (mycobacterial culture and PCR). Diagnostic potential of a multi-variable model combining clinical and ultrasound findings was explored using generalized mixed methods and random forest approach. (German trial registry DRKS00026636)Findings We included 541 participants of whom 102 (19%) had TB and 1% had HIV. “Focused assessment with sonography for HIV-associated tuberculosis” (FASH) showed moderate sensitivity (51%, 95%-CI 41-60) and specificity (70%, 95%-CI 66-74). Small consolidations on LUS showed high sensitivity (98%, 95%-CI 93-99), but were unspecific (14%, 95%-CI 11-18). Exploratory LUS variations showed higher specificity (e.g., large apical consolidations: sensitivity 22%, specificity 86%). Predictive modelling for ultrasound and clinical variables revealed an Area Under the Curve of 0.79 in the receiving operator curve.Interpretation Accuracy of ultrasound does not meet requirements of a stand-alone diagnostic or screening test. However, accuracy for some ultrasound findings is comparable with CXR. Additionally, ultrasound may aid disease severity assessment and microbiological sampling strategies. Research into alternative analyses (e.g., artificial intelligence) may enable wider applications.Funding Grant TTU 02.911, German Center for Infection Research (Deutsches Zentrum für Infektionsforschung).Research in context Before undertaking the study, LUS for TB had been assessed in a small number of studies limited with uncertain ultrasound characterization of TB-related findings with lack of adequate terminology and unclear specificity for TB. FASH-studies in HIV+ and few studies in HIV- have shown moderate sensitivity and specificity, but the study design and reference standards were not robust enough for generalizability.Our ultrasound study of LUS and FASH has a prospective cohort from a TB-endemic setting (India), we recruited 541 participants, the largest such cohort. This study brings to the body of evidence novel findings, backed by a robust study design and using a comprehensive reference standard. We were able to describe accuracy in a predominantly HIV-negative cohort of patients with presumed TB disease and compared our index testing protocol with the CXR, the most commonly used imaging modality. The implications from our study were that no single finding or combination of findings on LUS reached target product profiles (TPP) proposed by WHO, suggesting LUS as triage or diagnostic tool is too non-specific. The FASH accuracy in our study was in line with previous data, this study provides for it a solid foundation. The accuracy of submodules of LUS and FASH reaches that of CXR. Roles for ultrasound in TB care may lie in aiding diagnosis, assessment of disease severity, guiding of microbiological sampling or therapy monitoring. Further studies should focus on the accuracy of LUS in people living with HIV and children, evaluating ultrasound as a part of a diagnostic algorithm and the use of artificial intelligence to improve the yield of TB-POCUS.

RR:C19 Evidence Scale rating by reviewer:

  • Strong. The main study claims are very well-justified by the data and analytic methods used. There is little room for doubt that the study produced has very similar results and conclusions as compared with the hypothetical ideal study. The study’s main claims should be considered conclusive and actionable without reservation.

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Review: In this manuscript, the authors evaluate the utility of lung and abdominal ultrasound as diagnostic tools for tuberculosis in non-HIV-infected persons in India. They conclude that POCUS does not meet criteria for a standalone diagnostic test.

Point-of-care ultrasound (POCUS) has gained prominence as a valuable tool in a variety of clinical settings, and a robust body of literature supports its use in the diagnosis of pneumonia, particularly in children.  The technology offers several advantages over chest radiography, including portability, ease of use, lack of radiation exposure, cost, and availability in a variety of settings.  However, its use to determine specific etiologies of lung infections (e.g. tuberculosis), has not been well studied.  The authors of the study under review examined a prospective cohort in India consisting of 541 patients, nearly all HIV-negative, to determine the overall accuracy of POCUS as a diagnostic modality, comparing it to chest radiography and using mycobacterial culture and PCR as the diagnostic reference standard.  They found that sensitivity and specificity of ultrasound were modest (51% and 70%, respectively.

The study was carefully done, and the data were rigorously and properly analyzed.  In many ways, the findings are not altogether surprising, as parenchymal infiltrates and consolidation are hallmarks of pulmonary infections generally and are not specific to TB.  The finding that large apical consolidations detected by ultrasound were more specific (specificity 86%) makes sense, but the sensitivity of this finding was quite low (22%).  

There are some important limitations to the study.  India in general is a high prevalence country for TB, and the results obtained might not be applicable or reflective of an experience in other settings.  It might have been helpful for the authors to have included in their discussion a Bayesian analysis (likelihood ratios, positive/negative predictive values, etc.) that would give the reader a better sense of the utility of the test in settings with different prior probabilities of a TB diagnosis.  Similarly, the study was largely carried out at referral hospitals, and the results also for that reason might not be applicable in more primary care settings.

Overall, this is a valuable contribution to the literature and highlights some of the potential strengths of POCUS in the diagnosis of TB as well as the current limitations that make it inadequate as a standalone test for routine clinical use.

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