Limitations of the TST include:
- It can take weeks post-exposure (and subsequent development of infection) for the immune system to react.
- Two visits are required. The individual must return in 48-72 hours to a health care provider who is trained to read, measure, and interpret any reaction at the site of the injection.
- The BCG vaccine may cause a false-positive TST reaction, due to cross-reacting bacteria including those used to manufacture BCG.
- The PPD used in the TST is a mix of protein fragments derived from patients with TB disease, and thus poor specificity is problematic.
- Reading the TST is subject to interpretation by the health care provider.
- The TST may prompt boosting. (Boosting may occur as a result of old infection of MTB making it difficult to differentiate from a new conversion.)
- Immunosuppressed individuals may not mount an immune response.
