We would like to highlight an update in the diagnostic approach to tuberculosis (TB) investigation. While smear microscopy for acid fast bailli (AFB) has long been used for Mycobacterium tuberculosis complex (MTB) detection, it is no longer recommended as the initial rapid diagnostic test due to its low sensitivity and inability to distinguish MTB from non-tuberculous mycobacteria (NTM).
According to the World Health Organization (WHO), smear microscopy can miss a significant number of TB cases, particularly in individuals with low bacillary load such as children, people living with HIV, and those with extrapulmonary TB. Microscopy also does not detect drug resistance. The WHO now recommends rapid molecular tests, TB PCR (e.g. GeneXpert), as the initial diagnostic test for all individuals being evaluated for TB, offering improved sensitivity and specificity, rapid identification of MTB and the detection of rifampicin and/or isoniazid resistance. However, a negative PCR result does not rule out TB, especially in cases with low bacterial load or extrapulmonary involvement. In such cases, TB culture remains essential.
Optimizing TB Diagnostics