New technologies for diagnosing active TB: the VANTDET diagnostic accuracy study
Authors: Halliday Alice , Jain Pooja , Hoang Long , Parker Robert , Tolosa-Wright Mica , Masonou Tereza , Green Nathan , Boakye Aime , Takwoingi Yemisi , Hamilton Shea , Mandagere Vinay , Fries Anastasia , Coin Lachlan , Deeks Jon , White Peter J , Levin Michael , Beverley Peter , Kon Onn Min , Lalvani Ajit 
Published: April 2021

Background
Tuberculosis (TB) is a devastating disease for which new diagnostic tests are desperately needed.

Objective
To validate promising new technologies [namely whole-blood transcriptomics, proteomics, flow cytometry and quantitative reverse transcription-polymerase chain reaction (qRT-PCR)] and existing signatures for the detection of active TB in samples obtained from individuals with suspected active TB.

Design
Four substudies, each of which used samples from the biobank collected as part of the interferon gamma release assay (IGRA) in the Diagnostic Evaluation of Active TB study, which was a prospective cohort of patients recruited with suspected TB.

Setting
Secondary care.

Participants
Adults aged ≥ 16 years presenting as inpatients or outpatients at 12 NHS hospital trusts in London, Slough, Oxford, Leicester and Birmingham, with suspected active TB.

Interventions
New tests using genome-wide gene expression microarray (transcriptomics), surface-enhanced laser desorption ionisation time-of-flight mass spectrometry/liquid chromatography–mass spectrometry (proteomics), flow cytometry or qRT-PCR.

Main outcome measures
Area under the curve (AUC), sensitivity and specificity were calculated to determine diagnostic accuracy. Positive and negative predictive values were calculated in some cases. A decision tree model was developed to calculate the incremental costs and quality-adjusted life-years of changing from current practice to using the novels tests.

Results
The project, and four substudies that assessed the previously published signatures, measured each of the new technologies and performed a health economic analysis in which the best-performing tests were evaluated for cost-effectiveness. The diagnostic accuracy of the transcriptomic tests ranged from an AUC of 0.81 to 0.84 for detecting all TB in our cohort. The performance for detecting culture-confirmed TB or pulmonary TB was better than for highly probable TB or extrapulmonary tuberculosis (EPTB), but was not high enough to be clinically useful. None of the previously described serum proteomic signatures for active TB provided good diagnostic accuracy, nor did the candidate rule-out tests. Four out of six previously described cellular immune signatures provided a reasonable level of diagnostic accuracy (AUC = 0.78–0.92) for discriminating all TB from those with other disease and latent TB infection in human immunodeficiency virus-negative TB suspects. Two of these assays may be useful in the IGRA-positive population and can provide high positive predictive value. None of the new tests for TB can be considered cost-effective.

Limitations
The diagnostic performance of new tests among the HIV-positive population was either underpowered or not sufficiently achieved in each substudy.

Conclusions
Overall, the diagnostic performance of all previously identified ‘signatures’ of TB was lower than previously reported. This probably reflects the nature of the cohort we used, which includes the harder to diagnose groups, such as culture-unconfirmed TB or EPTB, which were under-represented in previous cohorts.

Future work
We are yet to achieve our secondary objective of deriving novel signatures of TB using our data sets. This was beyond the scope of this report. We recommend that future studies using these technologies target specific subtypes of TB, specifically those groups for which new diagnostic tests are required.

Funding
This project was funded by the Efficacy and Mechanism Evaluation (EME) programme, a MRC and NIHR partnership.