Comparative evaluation of nitrate reductase assay with conventional proportion method for isoniazid and rifampicin susceptibility testing in smear positive pulmonary tuberculosis patients

Abstract

With the surge of multidrug-resistant tuberculosis (MDR-TB) strains there is an escalating need for precise and cost-effective methods for a precipitous diagnostic and drug susceptibility testing (DST), chiefly in resource limited countries where tuberculosis is endemic. To find out the susceptibility pattern of Isoniazid (INH) and Rifampicin (RMP) in smear positive cases of pulmonary TB at MMIMSR Mullana and to evaluate the sensitivity and specificity of nitrate reductase assay (NRA) with standard proportion method for INH and RMP susceptibility testing. A cross sectional test validation study was carried out at Mycobacteriology division in the Department of Microbiology on 100 smear positive sputum samples from pulmonary tuberculosis patients.In comparison with L.J proportion method, NRA showed sensitivity, specificity, PPV, NPV, accuracy of 100%, 98.64%, 87.50%, 100%, and 98.76% respectively for INH. The sensitivity, specificity, PPV, NPV, accuracy of NRA compared to PM for RMP was 100%, 97.33%, 75.00%, 100%, 97.53% respectively. Direct NRA is simple, easy to perform, prompt, reasonably less expensive, without requisite of expensive reagents and advanced instrumentation. It is highly specific and sensitive technique in the detection of drug resistant TB when tested in parallel with the proportion method. Therefore, NRA may be routinely employed in TB laboratories in developing countries for drug susceptibility testing of .