Diagnostic accuracy of urinary lipoarabinomannan antigen detection for the diagnosis of pulmonary and extra pulmonary tuberculosis (EPTB) in HIV negative population

BACKGROUND: Urine antigen testing seems promising tool to detect tuberculosis but data is scarce for pulmonary and extrapulmonary tuberculosis in HIV negative population. AIMS: This prospective cross-sectional study was designed to assess the urinary lipoarabinomannan antigen (LAM) diagnostic accuracy of pulmonary and extrapulmonary tuberculosis in HIV negative population. MATERIALS & METHODS: Suspected pulmonary (PTB) and extrapulmonary tuberculosis (EPTB) patients were enrolled and samples were subjected to routine diagnostic modalities. Urine samples were subjected to LAM test using lateral flow assay of Abbott TB LAM & results were statistically evaluated to gold standard culture, microbiological reference standards (MRS). RESULTS: Total 224 patients of suspected tuberculosis were enrolled in the study (23.21 % PTB and 76.79 % EPTB). Microbiologically confirmed tuberculosis was detected in 44 (19.6 %), PTB (48.0 %) & EPTB (11.0 %) cases. Mycobacterium tuberculosis was detected in ZN stain (16.5 %), MGIT liquid culture (14.7 %), Gene-Xpert MTB/Rif (17.4 %), urinary LAM (22.7 %). Sensitivity, specificity, PPV and NPV of urine LAM against the gold standard test (MGIT) were 60.61 %, 83.77 %, 39.22 %, 92.49 %; and as per the MRS criteria these values were 48.0 %, 84.5 %, 47.1 %, 85.0 % respectively. Among smear positive samples sensitivity, specificity, PPV, NPV of LAM were 65.5 %, 50.0 %, 82.6 %, 28.6 % respectively. CONCLUSION: Urine LAM performed better than previously reported in HIV-negative populations but remains suboptimal as a point-of-care test. This study showed higher sensitivity and PPV for pulmonary TB in MRS smear-positive cases, better specificity and NPV for extrapulmonary TB, good performance in smear-negative extrapulmonary TB, and promising utility in unconfirmed TB.