COMPARATIVE ASSESSMENT OF URINE LIPOARABINOMANNAN ASSAY AND ZIEHL NEELSEN SPUTUM SMEAR MICROSCOPY AS TUBERCULOSIS DIAGNOSTIC TOOLS IN NNEWI, NIGERIA

Abstract

Introduction. Tuberculosis (TB) remains a major public health issue worldwide, with about 8.0 million new cases and 2.0 million deaths yearly, the burden being more in the developing countries partly due to missed or improper diagnosis. Most available methods for TB diagnosis have one shortcoming or the other. The current detection rate of TB is far below set target, making it imperative for diagnostic tests that are rapid and accurate.

Aim: To assess the accuracy of urinary lipoarabinomannan (LAM) antigen and ZN microscopy assays in detecting MTB using Gene Xpert MTB/RIF as the gold standard.

Methodology: A total of 200 participants, 109 males and 91 females, accessing care at the TB (DOTS) Center of Nnamdi Azikiwe University Teaching Hospital, Nnewi were tested for TB using urinary LAM ELISA, ZN sputum microscopy and Xpert MTB/RIF. All the participants were recruited sequentially as they presented at the DOTS clinic. This is an experimental cross sectional study and all the data obtained were analysed using SPSS (statistical package for social sciences), version 20.

Results: ZN microscopy with a sensitivity of 80.0%, specificity of 91.1%, positive predictive value of 90.0%, negative predictive value of 82.2%, and diagnostic accuracy of 85.6% was found to be comparatively superior to LAM ELISA which had sensitivity of 13.3 %, specificity of 71.1%, positive predictive value of 31.6%, negative predictive value of 45.1 and diagnostic accuracy of 42.2%. Positivity rate with LAM ELISA was higher in HIV-positive patients (30.8 %) than in the HIV negative patients (20.0%).

Conclusion: LAM antigen assay does not appear to be very useful as a stand-alone test for TB due to its variable sensitivity and specificity compared to the gold standard in TB diagnosis which is smear microscopy. Smear microscopy should be optimized for enhanced performance in view of its superiority over LAM ELISA as noted in this study.