Detection of INH resistance from these isolates was missed by the MTBDRplus assay; this demonstrated the significance of adding the ahpC locus for detecting INH resistance. Our study found a rather small increase (4.5%) in sensitivity contributed by ahpC. However, any increase in the detection of INH resistance reduces ineffective INH treatment and prophylaxis and is welcomed by clinicians and public health authorities, especially when the specificity remains 100%.