Development of accurate non-sputum-based diagnostic tests for tuberculosis: an ongoing challenge

Tuberculosis is the leading cause of death, admission to hospital, and inpatient mortality in adults with HIV. Progress towards ending tuberculosis mortality has been reversed by the COVID-19 pandemic, with an estimated 187 000 deaths in individuals with HIV-associated tuberculosis in 2021.1WHOGlobal tuberculosis report 2022. World Health Organization, Geneva2022Google Scholar To decrease this mortality, accurate and affordable diagnostic tests that are rapid and available at, or close to, the point of care are urgently needed; these tests could ensure appropriate and timeous initiation of tuberculosis treatment in people with HIV who might have rapid clinical deterioration without treatment.2WHOHigh-priority target product profiles for new tuberculosis diagnostics: report of a consensus meeting. World Health Organization, Geneva2014Google Scholar There is a clear need for tests that are non-sputum based (eg, urine or blood) in people with HIV, since risk of mortality is disproportionately high in this group as a result of a reduced ability to produce sputum or extra-pulmonary disease.2WHOHigh-priority target product profiles for new tuberculosis diagnostics: report of a consensus meeting. World Health Organization, Geneva2014Google Scholar The commercially available and WHO-recommended point of care test for urine is the Alere Determine AlereLAM Ag test (AlereLAM; Abbott, Waltham, MA, USA). AlereLAM has been shown to reduce mortality when included in the clinical investigation of seriously ill people with HIV who are admitted to hospital3Peter JG Zijenah LS Chanda D et al.Effect on mortality of point-of-care, urine-based lipoarabinomannan testing to guide tuberculosis treatment initiation in HIV-positive hospital inpatients: a pragmatic, parallel-group, multicountry, open-label, randomised controlled trial.Lancet. 2016; 387: 1187-1197Summary Full Text Full Text PDF PubMed Scopus (169) Google Scholar, 4Gupta-Wright A Corbett EL van Oosterhout JJ et al.Rapid urine-based screening for tuberculosis in HIV-positive patients admitted to hospital in Africa (STAMP): a pragmatic, multicentre, parallel-group, double-blind, randomised controlled trial.Lancet. 2018; 392: 292-301Summary Full Text Full Text PDF PubMed Scopus (115) Google Scholar and is easy and rapid to perform. The utility of the test is constrained by inadequate diagnostic sensitivity, which is estimated at 62% in patients admitted to hospital and 31% in outpatients.5Bjerrum S Schiller I Dendukuri N et al.Lateral flow urine lipoarabinomannan assay for detecting active tuberculosis in people living with HIV.Cochrane Database Syst Rev. 2019; 10CD011420PubMed Google Scholar A next generation, point-of-care urine lipoarabinomannan (LAM) test, the Fujifilm SILVAMP TB LAM (FujiLAM; Fujifilm, Tokyo, Japan) assay has been developed, which incorporates optimised capture antibodies and a silver amplification step to improve sensitivity and specificity. In various cohorts, the FujiLAM assay performed on urine from biobank sources improved sensitivity by 20–30% and maintained similar specificity when compared with AlereLAM.6Broger T Nicol MP Székely R et al.Diagnostic accuracy of a novel tuberculosis point-of-care urine lipoarabinomannan assay for people living with HIV: a meta-analysis of individual in- and outpatient data.PLoS Med. 2020; 17e1003113Crossref PubMed Scopus (33) Google Scholar, 7Muyoyeta M Kerkhoff AD Chilukutu L Moreau E Schumacher SG Ruhwald M Diagnostic accuracy of a novel point-of-care urine lipoarabinomannan assay for the detection of tuberculosis among adult outpatients in Zambia: a prospective cross-sectional study.Eur Respir J. 2021; 582003999Crossref PubMed Scopus (7) Google Scholar Evidence on the diagnostic accuracy in real time and with fresh urine is still needed before WHO endorsement of this new test and its wider uptake. In this issue of The Lancet Global Health, Helena Huerga and colleagues8Huerga H Bastard M Lubega AV et al.Novel FujiLAM assay to detect tuberculosis in HIV-positive ambulatory patients in four African countries: a diagnostic accuracy study.Lancet Glob Health. 2023; 11: e126-e135Summary Full Text Full Text PDF Google Scholar report the results of a multicentre, diagnostic accuracy study comparing FujiLAM and AlereLAM using fresh urine samples obtained from ambulatory HIV-positive individuals. The study was done in Uganda, Kenya, Mozambique, and South Africa, in two groups at high risk of tuberculosis: group 1 included individuals with signs or symptoms of tuberculosis, irrespective of CD4 T-cell count, and group 2 included asymptomatic individuals who had advanced stage HIV disease (ie, CD4 count ≤200 cells per μL or WHO clinical stage 3 or 4). Tuberculosis was microbiologically confirmed in 96 (9·4%) of 1022 patients in group 1 (median CD4 count 528 cells per μL [IQR 272–770]) and 18 (3·3%) of 542 patients in group 2 (median CD4 count 128 cells per μL [66–181]). Only three-quarters of individuals in group 1 and fewer than 10% of individuals in group 2 could spontaneously produce sputum, whereas almost all participants could produce a urine sample. Diagnostic accuracy was assessed against two reference standards: FujiLAM had an overall sensitivity of 60% (95% CI 51–69) against the microbiological reference standard and 48% (40–56) against the composite reference standard compared with a sensitivity of 40% (31–49) against the microbiological reference standard and 38% (31–46) against the composite reference standard for AlereLAM. FujiLAM had an overall specificity of 87% (85–89) against the microbiological reference standard and 90% (88–92) against the composite reference standard compared with specificity of 86% (84–88) against the microbiological reference standard and 95% (94–96) against the composite reference standard for AlereLAM. These findings are broadly consistent with the findings of previous retrospective studies using specimens obtained from biobanks.6Broger T Nicol MP Székely R et al.Diagnostic accuracy of a novel tuberculosis point-of-care urine lipoarabinomannan assay for people living with HIV: a meta-analysis of individual in- and outpatient data.PLoS Med. 2020; 17e1003113Crossref PubMed Scopus (33) Google Scholar, 7Muyoyeta M Kerkhoff AD Chilukutu L Moreau E Schumacher SG Ruhwald M Diagnostic accuracy of a novel point-of-care urine lipoarabinomannan assay for the detection of tuberculosis among adult outpatients in Zambia: a prospective cross-sectional study.Eur Respir J. 2021; 582003999Crossref PubMed Scopus (7) Google Scholar A high proportion of participants were unclassifiable by the microbiological reference standard (458 [29·3%] of 1564 patients) and composite reference standard (303 [19·4%]), which adds a degree of uncertainty to the findings. In a post-hoc analysis diagnostic accuracy varied by FujiLAM lot, with approximately 20% variation in both sensitivity and specificity depending on which lot was being used. Variation by lot has also been detected in a multinational prospective FujiLAM diagnostic accuracy study.9Székely R Sossen B Mukoka M et al.Multicentre accuracy trial of FUJIFILM SILVAMP TB LAM test in people with HIV reveals lot variability.medRxiv. 2022; (published online Sept 9.) (preprint).https://doi.org/10.1101/2022.09.07.22278961Google Scholar In that study, repeat testing with different FujiLAM lots on the same urine sample yielded different results. Based on their findings, Huerga and colleagues concluded that the FujiLAM assay has improved sensitivity and can potentially broaden the patient population that would benefit from point-of-care urine-based tuberculosis diagnosis. However, they advised that lot variability needs to be addressed before clinical use of the assay. Although the lot variation identified in these two studies is a setback, results of the ultrasensitive laboratory-based electrochemiluminescence LAM assay (Meso Scale Diagnostics, Rockville, MD, USA), which incorporates the same optimised antibodies used to design FujiLAM, show consistently high diagnostic accuracy,9Székely R Sossen B Mukoka M et al.Multicentre accuracy trial of FUJIFILM SILVAMP TB LAM test in people with HIV reveals lot variability.medRxiv. 2022; (published online Sept 9.) (preprint).https://doi.org/10.1101/2022.09.07.22278961Google Scholar, 10Sigal GB Pinter A Lowary TL et al.A novel sensitive immunoassay targeting the 5-methylthio-D-xylofuranose–lipoarabinomannan epitope meets the WHO's performance target for tuberculosis diagnosis.J Clin Microbiol. 2018; 56: e01338-e01348Crossref PubMed Scopus (70) Google Scholar providing reassurance that improved urine LAM diagnostics remain possible. Further research on updated, consistent versions of FujiLAM and on other non-sputum-based rapid diagnostic tests is necessary to support global efforts to reduce deaths due to HIV-associated tuberculosis. The ultimate goal is a test with high diagnostic accuracy and reproducibility that can be done at, or close to, the point of care, on a sample that can be reliably obtained, thereby allowing for diagnosis and treatment initiation for HIV-associated tuberculosis at an individual's initial contact with the health system. A clear and bold agenda with sufficient investment to drive this research forward needs to be sustained. We declare no competing interests. GM was supported by the Wellcome Trust (grants 214321/Z/18/Z, 203135/Z/16/Z), and the South African Research Chairs Initiative of the Department of Science and Technology and National Research Foundation of South Africa (grant 64787). Novel FujiLAM assay to detect tuberculosis in HIV-positive ambulatory patients in four African countries: a diagnostic accuracy studyNext-generation, higher sensitivity urine-lipoarabinomannan assays are potentially promising tests that allow rapid tuberculosis diagnosis at the point of care for HIV-positive patients. However, the variability in accuracy between FujiLAM lot numbers needs to be addressed before clinical use. Full-Text PDF Open Access