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

Abstract

Background: A novel, rapid, point-of-care urine-based lipoarabinomannan assay (Fujifilm SILVAMP TB-LAM, "FujiLAM") has previously demonstrated substantially higher sensitivity for tuberculosis (TB) compared to the commercially-available Determine TB-LAM assay using bio-banked specimens. However, FujiLAM has not been prospectively evaluated using fresh urine specimens. Therefore, we determined the diagnostic accuracy of FujiLAM among HIV-positive and HIV-negative outpatients with presumptive TB in Zambia. Methods: Adult (>18 years) presumptive TB patients presenting to two outpatient public health facilities in Lusaka, were included. All patients submitted sputa samples for smear-microscopy, Xpert Ultra and Mycobacterial culture and urine samples for the FujiLAM assay. Microbiologically-confirmed TB was defined by the detection of Mycobacterium tuberculosis in sputum using culture; this served as the reference standard to assess the diagnostic accuracy of FujiLAM. Results: 151 adults with paired sputum microbiologic tests and urine FujiLAM results were included; 45% were HIV-positive. Overall, 34/151 (23%) patients had culture-confirmed pulmonary TB. The overall sensitivity and specificity of FujiLAM was 77% (95%CI: 59-89) and 92% (95%CI: 86-96), respectively. FujiLAM"s sensitivity among HIV-positive patients was 75% (95%CI: 43-95) compared to 75% (95%CI: 51-91) among HIV-negative patients. The sensitivity of FujiLAM in patients with smear-positive, confirmed pulmonary TB was 87% (95%CI: 60-98) compared to 68% (95%: 43-87) among patients with smear-negative, confirmed pulmonary TB. Conclusions: FujiLAM demonstrated high sensitivity for the detection of TB among both HIV-positive and HIV-negative adults and also demonstrated good specificity despite the lack of systematic extra-pulmonary sampling to inform a comprehensive microbiological reference standard.