The diagnostic utility of line probe assays for multidrug-resistant tuberculosis

Owing to the burden of multidrug-resistant tuberculosis, molecular techniques have been approved by the WHO for the rapid diagnosis of the same. The objectives of this prospective, diagnostic study, conducted at Christian Medical College, a tertiary care center in South India, were to compare the performance of line probe assay (GenoTypeMTBDRplus) with culture, as well as the Xpert MTB/Rif assay on sputum samples. Ninety-one consecutive suspects of multidrug-resistant pulmonary tuberculosis patients from January 2013 to June 2013 were enrolled in this study and the results of line probe assay compared to culture and Xpert MTB/Rif. Compared to culture, the assay demonstrated a sensitivity and specificity of 81.5% (95%CI 67.4-91.1%) and 87.5% (95%CI 71-96.5%) for the detection of tuberculosis, with sensitivity and specificity of 100% (95%CI 85.2-100%) and 93.8% (95%CI 69.8-99.8%), respectively, for rifampicin resistance. For isoniazid resistance, sensitivity and specificity were 89.3% (95%CI 71.8-97.7%) and 100% (95%CI 71.5-100%), respectively. Compared to Xpert MTB/Rif assay, the assay showed a sensitivity of 80% (95%CI 68.2-88.9%) and specificity of 100% (95%CI 85.8-100%) for the detection of tuberculosis a sensitivity of 94.3% (95%CI 80.8-99.3%) and specificity of 94.1% (95%CI 71.3-99.9%) for rifampicin resistance was attained. This assay performed well on smear positive samples, but poorly on smear negative and scanty samples, and can serve as a rapid diagnostic tool, particularly in isoniazid monoresistant cases of tuberculosis, which are not diagnosed by Xpert MTB/Rif.