Conventional Drug Susceptibility Test (DST)

• In conventional DST, which uses cultured bacilli, the laboratory procedure determines if the M. tuberculosis strain grows in the presence of anti-TB drugs.


• If the strain grows, it is said to be resistant to that drug. Conventional DST methods, subsequent to primary culture, can take an additional 4 to 6 weeks.


• Rapid, molecular DSTs (Xpert MTB/RIF and the line probe assay) can diagnose drug resistance in just a few hours. However, they may miss a small proportion of patients who are truly drug resistant (and would be detected using a culture).


• New tools such as Xpert MTB/RIF should be used when feasible because their infrastructure requirements are significantly less than those required for culture and the rapid diagnosis allows for quicker treatment initiation for patients.