Improving the Sensitivity of the Xpert MTB/RIF Assay on Sputum Pellets by Decreasing the Amount of Added Sample Reagent: a Laboratory and Clinical Evaluation

摘要: ABSTRACT The Xpert MTB/RIF (Xpert) assay permits rapid near-patient detection of Mycobacterium tuberculosis in sputum; however, the test sensitivity remains suboptimal paucibacillary specimens that are negative for acid-fast bacilli using smear microscopy. testing includes dilution with sample reagent, and when processed sputum pellets tested, recommended reagent/pellet ratio is 3:1. We evaluated whether a decreased 2:1 increased compared to limit was determined by inoculating serial dilutions M. into samples, preparing pellets, each pellet at both reagent ratios. Processed obtained from culture-positive clinical were also tested Among spiked 1,478 CFU/ml (95% confidence interval [CI], 1,211 1,943) 3:1 832 CI, 671 1,134) 2:1. proportion which detected greater than almost all numbers CFU/ml; this difference most prominent lower CFU/ml. 134 concentrated study, overall (80% versus 72%; P = 0.03) smear-negative (67% 58%; 0.12). For detection, especially specimens. Our study supports use pellets.