Culture Drug Susceptibility Testing [CDST]

Culture Drug Susceptibility Testing (CDST) is a growth-based phenotypic method used to check the susceptibility of Mycobacterium tuberculosis strains to various first and second line anti-TB drugs. Mycobacterial resistance to a particular drug is identified if there is growth observed in culture in presence of that drug.

In NTEP CDST is the standard method to detect resistance in samples of patients who have tested positive on followup. While CDST is possible on both Solid and Liquid culture, currently, the NTEP utilizes only liquid culture as a method for DST, due to faster Turn around times.

CDST testing services are available under NTEP in designated, specialized laboratories called CDST Labs both in public and private sector. Currently there are 80 such laboratories (60 certified for First Line and 49 for Second line drugs). Such designated laboratories are subject to regular external quality assessment, often by the National Reference Laboratory at that region.

Quality assured DST to R, H, Z, Mfx, Lfx, Lzd, Am, Km and Cm are available across the country. 

Resources

• Guidelines for Programmatic Management of Drug-resistant Tuberculosis in India, 2021.
• Training Manual for Mycobacterium tuberculosis Culture & Drug Susceptibility Testing, NTEP, 2009.
• RNTCP Laboratory Network Overview, CTD, 2009.