Urine lipoarabinomannan concentrations among HIV-negative adults with pulmonary or extrapulmonary tuberculosis disease in Vietnam

Abstract

Lipoarabinomannan (LAM) is a promising target biomarker for diagnosing subclinical and clinical tuberculosis (TB). Urine LAM (uLAM) testing using rapid diagnostic tests (RDTs) has been approved for people living with HIV (PLWH), however there is limited data regarding uLAM levels in HIV-negative (HIV-ve) adults with clinical TB. We conducted a clinical study of adults presenting with clinical TB-related symptoms at the National Lung Hospital in Hanoi, Vietnam. The uLAM concentrations were measured using electrochemiluminescent (ECL) immunoassays and compared to a microbiological reference standard (MRS) using GeneXpert Ultra and TB culture testing. Estimated uLAM concentrations above plate specific calculated limit of detection (LOD) were considered uLAM positive. Additional microbiological testing was conducted for possible extrapulmonary TB (EPTB). Among 745 participants enrolled, 335 (44.9%) participants with presumptive pulmonary TB (PTB) and 6 (11.3%) participants with presumptive EPTB had confirmed TB disease. Overall, the S/A antibody pair had a sensitivity of 39% (95% Confidence Interval [CI] 0.33, 0.44) and a specificity of 97% (95% CI 0.96, 0.99) compared to the MRS. The F/A antibody pair had a sensitivity of 41% (95% CI 0.35, 0.47) and a specificity of 79% (95% CI 0.75, 0.84). S/A provided greater discriminatory ability compared to F/A for both individuals with presumptive PTB (AUROC: 0.74 vs 0.63, p<0.0001) and presumptive EPTB (0.76 vs 0.54, p = 0.045) when using the MRS. Among HIV-ve participants in an adult cohort in Vietnam, the concentrations of uLAM remained relatively low for people with clinical TB, which may present challenges for improving RDT sensitivity.

Fig 1. A STARD accuracy flowchart of the recruitment and diagnostic classification of the study subjects from October 2021 to April 2022.

HIV, human immunodeficiency virus; Presumptive PTB, Presumptive Pulmonary TuBerculosis; Presumptive EPTB, Presumptive Extra Pulmonary TuBerculosis; Xpert, GeneXpert MTB/RIF Ultra.

Fig 2. The range of uLAM concentrations quantitated by the ECL immunoassay using antibody pairs S/A and F/A, stratified by MRS status and cohort (N = 745).

The uLAM concentrations as measured using the S/A and F/A antibody pairs in both MRS positive (red) and MRS negative (blue), stratified by cohort status. The data was scored as both the number of positive results observed and with the median concentration of uLAM determined from the uLAM positive samples of all positive results using the ECL assays.

Fig 3. Receiver operating characteristic curves including sensitivity and specificity 95% CIs comparing estimated uLAM concentrations (pg/mL) derived from the S/A and F/A Ab pairs to MRS.

ROCs for presumptive PTB (n = 692) and EPTB (n = 53) are depicted on the left & right, respectively. The ROC for S/A is shown by the solid blue line, while the ROC for F/A is shown by the dashed red line. 95% CIs for threshold sensitivity is depicted vertically by the shaded area, with 95% CI threshold specificity shown by horizontal bars. Abbreviations: CI, confidence interval; S/A, S4-20/A194-01; F/A, FIND28/A194-01; PTB, pulmonary tuberculosis; MRS, microbiological reference standard; CRS, clinical reference standard; EPTB, extra pulmonary tuberculosis.