f a gold standard test for diagnosis of LTBI, current clinical management of patients with IMID requiring anti-TNF therapy involves checking for a history of untreated or partially treated TB, risk-stratification for exposure to cases of active TB, evidence of residual changes indicative of prior TB infection on a chest radiograph and a tuberculin skin test (TST).

The TST is a measure of the delayed-type hypersensitivity reaction to intradermal inoculation of purified protein derivative (PPD), a crude mixture of more than 200 *M. tuberculosis* proteins. Because antigens within PPD are also found in other mycobacteria, the TST suffers from poor specificity in bacille Calmette--Guérin (BCG)-vaccinated persons. Moreover, the sensitivity of the tuberculin skin test used to diagnose LTBI is compromised in patients on immunosuppressive therapy with a high rate of false-negative TST test results. For example, in a Peruvian study, the size of the TST response was significantly lower and the proportion negative (i.e. \< 5 mm) to TST was significantly higher in patients with RA compared to healthy immunocompetent controls (median size PPD induration 4.5 vs 11.5 mm *P* \< 0.01; 79/112 (70.6%) vs 25/96 (26%) *P* \< 0.01, respectively) [@bib6]. Logistical hurdles, including the need for a return visit to read the result of this in vivo test and operator variability in inoculation and reading of the result, also limit the effective use of TST.

Thus because almost all patients awaiting initiation of anti-TNF therapy are on immunosuppressive therapy [@bib1], the TST is not an appropriate test to screen for LTBI in patients with chronic inflammatory diseases. This concern around the interpretation of the TST in patients on disease modifying antirheumatic drugs (DMARDs) is reflected in British Thoracic Society guidelines from 2005 that recommended replacing TST with an individual risk--benefit calculation in patients with a normal chest radiograph balancing the population risk of LTBI in different groups based on age and