Ultra-sensitive urinary lipoarabinomannan (LAM) immunoassay for tuberculosis detection: a performance evaluation.

Abstract

The development of rapid non-sputum tests remains a global priority to accelerate Tuberculosis (TB) diagnosis and treatment initiation. The only WHO-recommended rapid diagnostic test (RDT), the Alere Determine TB Lipoarabinomannan Ag (AlereLAM) has suboptimal sensitivity. A laboratory-based electrochemiluminescence LAM assay (EclLAM) is the current sensitivity benchmark for RDT development and the gold standard for urinary LAM detection. We assessed the diagnostic accuracy of an ultra-sensitive, Plasmonic Fluor-linked Immunosorbent LAM assay (PFLISA-LAM) compared to Sputum Xpert MTB/RIF, sputum culture and urine EclLAM. We developed and evaluated the assay performance of PFLISA-LAM. Two sub-studies were conducted using banked urine samples: 1. Preclinical study using 337 well-characterised urine samples for cutoff determination and initial evaluation of the performance of PFLISA-LAM compared to sputum Xpert MTB/RIF and culture. 2. A Diagnostic accuracy assessment study using 77 blinded samples to evaluate the performance of PFLISA-LAM compared to EclLAM versus microbiological reference standard (MRS, Xpert positive and/or culture positive). PFLISA-LAM has a limit of detection (LOD) of 0.84 ± 0.9 pg/mL when detecting purified LAM spiked in urine. In the preclinical study, the optimal assay cutoff was determined to be 1.7 pg/mL. The sensitivities of PFLISA-LAM and sputum Xpert MTB/RIF compared to culture were 51% (95% confidence interval [CI]: 43%-59%) and 62% (95% CI: 53%-70%). The specificities of PFLISA-LAM and Xpert MTB/RIF were 99% (95% CI: 96%-100%) and 100% (95% CI: 100%-100%). Combining PFLISA-LAM and Xpert MTB/RIF test data, an improved sensitivity of 76% (95% CI: 69%-83%) can be achieved. In the diagnostic study, the sensitivities of EclLAM and PFLISA-LAM assays were 42% (95% CI: 27%-59%) and 73% (95% CI: 56%-85%). The specificities of EclLAM and PFLISA-LAM were 95% (95% CI: 85%-99%) and 98% (95% CI: 88%-100%). With better analytical and diagnostic sensitivity compared to EclLAM, PFLISA-LAM can better detect urinary LAM in TB-positive cases. PFLISA-LAM assay also demonstrated the capability to increase the diagnostic value in detecting urinary LAM, complementing molecular tests, achieving improved diagnostic outcome. We report no external financial support for conducting the study.