What is the role of newer diagnostic tests?
Ans: (i) Serological tests have poor sensitivity and specificity. Their sensitivity is highest in patients with smear positive disease and much lower among TB cases not detected by smear microscopy viz. sputum smear negative cases of pulmonary TB, extra-pulmonary TB, children diagnosed with TB and HIV infected TB cases. Also, these tests do not reliably distinguish active TB from dormant infection. (ii) Amplification tests e.g. polymerase chain reaction (PCR) are 95% sensitive in smear positive cases and only 50% sensitive in smear negative and culture positive cases. Though specificity is high, it is lower under field conditions. In addition, inability to distinguish viable from dead bacilli and high cost dissuade their use in developing countries. (iii) The Assay of cell-mediated immunity is highly complex.
