The understanding of the genetic basis of INH resistance is incomplete. The sensitivity of detecting INH resistance mutations from katG and the inhA promoter was only 82.7%, as shown in our previous study (11). To increase the sensitivity, we added ahpC in our PSQ panel. In a study (31) conducted by Huang et al., 18 of 28 MDR TB isolates possessed ahpC mutations alone or in addition to katG mutations outside of codon 315.