Abstract
BackgroundSimple immune capture assays that detect mycobacterial lipoarabinomannan (LAM) antigen in urine are promising new tools for the diagnosis of HIV-associated tuberculosis (HIV-TB). In addition, however, recent prospective cohort studies of patients with HIV-TB have demonstrated associations between LAM in the urine and increased mortality risk during TB treatment, indicating an additional utility of urinary LAM as a prognostic marker. We conducted a systematic review and meta-analysis to summarise the evidence concerning the strength of this relationship in adults with HIV-TB in sub-Saharan Africa, thereby quantifying the assay’s prognostic value.MethodsWe searched MEDLINE and Embase databases using comprehensive search terms for ‘HIV’, ‘TB’, ‘LAM’ and ‘sub-Saharan Africa’. Identified studies were reviewed and selected according to predefined criteria.ResultsWe identified 10 studies eligible for inclusion in this systematic review, reporting on a total of 1172 HIV-TB cases. Of these, 512 patients (44 %) tested positive for urinary LAM. After a variable duration of follow-up of between 2 and 6 months, overall case fatality rates among HIV-TB cases varied between 7 % and 53 %. Pooled summary estimates generated by random-effects meta-analysis showed a two-fold increased risk of mortality for urinary LAM-positive HIV-TB cases compared to urinary LAM-negative HIV-TB cases (relative risk 2.3, 95 % confidence interval 1.6–3.1). Some heterogeneity was explained by study setting and patient population in sub-group analyses. Five studies also reported multivariable analyses of risk factors for mortality, and pooled summary estimates demonstrated over two-fold increased mortality risk (odds ratio 2.5, 95 % confidence interval 1.4–4.5) among urinary LAM-positive HIV-TB cases, even after adjustment for other risk factors for mortality, including CD4 cell count.ConclusionsWe have demonstrated that detectable LAM in urine is associated with increased risk of mortality during TB treatment, and that this relationship remains after adjusting for other risk factors for mortality. This may simply be due to a positive test for urinary LAM serving as a marker of higher mycobacterial load and greater disease dissemination and severity. Alternatively, LAM antigen may directly compromise host immune responses through its known immunomodulatory effects. Detectable LAM in the urine is an independent risk factor for mortality among patients receiving treatment for HIV-TB. Further research is warranted to elucidate the underlying mechanisms and to determine whether this vulnerable patient population may benefit from adjunctive interventions.Electronic supplementary materialThe online version of this article (doi:10.1186/s12916-016-0603-9) contains supplementary material, which is available to authorized users.
Highlights
Simple immune capture assays that detect mycobacterial lipoarabinomannan (LAM) antigen in urine are promising new tools for the diagnosis of HIV-associated tuberculosis (HIV-TB)
We have demonstrated that detectable LAM in urine is associated with increased risk of mortality during TB treatment, and that this relationship remains after adjusting for other risk factors for mortality
Most studies enrolled patients in whom TB was the suspected diagnosis based on clinical presentation, three studies were done in patients due to start anti-retroviral therapy (ART), and one study was restricted to patients with a TB diagnosis (Table 1)
Summary
Simple immune capture assays that detect mycobacterial lipoarabinomannan (LAM) antigen in urine are promising new tools for the diagnosis of HIV-associated tuberculosis (HIV-TB). In addition to commercially available enzyme-linked immunosorbent assays (ELISA), a simple, low-cost and rapid lateral flow point-of-care assay has been developed (Determine TB-LAM; Alere Inc., Waltham, MA, USA). This is undergoing impact evaluation as part of the diagnostic algorithms for HIV-TB in clinical trials in sub-Saharan Africa [14,15,16], and WHO have conditionally recommended its use to assist in TB diagnosis in hospitalised patients with low (≤100 cells/μl) CD4 cell counts or patients who are seriously ill [17]
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