 The second tier is constituted by Intermediate Reference Laboratories(IRL) and Culture and Drug Susceptibility Testing (C&DST) Labs, which provide advanced DST facilities and supervisory support to the first tier.The National Reference Laboratories constitute the third tier, and provide quality assurance and certification services for C&DST labs and co-ordinate with WHO Supra National Reference Laboratory Network.In addition to the above, Chest Radiography, available at tertiary and secondary healthcare levels, also play an important role in screening for Tuberculosis signs and clinical diagnosis.