A novel assay for screening patients for latent tuberculosis infection prior to anti-TNF therapy

Screening for latent tuberculosis (TB) infection (LTBI) prior to anti-tumor necrosis factor (TNF) therapy is complicated by the decreased sensitivity of the purified protein derivative tuberculin skin test in immunosuppressed patients, as well as the poor specificity of the tuberculin skin test in bacillus Calmette-Guérin (BCG)-vaccinated patients. Interferon-gamma-release assays that utilize specific TB antigens (e.g. ESAT-6/CFP-10) have greater specificity for LTBI, but their relative sensitivity is unknown in the setting of immune suppression. Dinser et al. evaluated a novel flow-cytometric interferon-gamma detection assay in 97 patients with inflammatory arthritis during LTBI screening for anti-TNF therapy. Overall, 39% of patients had purified protein derivative reactivity in vitro versus 14% cutaneously, and 16% exhibited reactivity in vitro to ESAT-6/CFP-10. The results suggest that flow cytometry using TB-specific antigens might eventually provide another tool for diagnosing LTBI in patients undergoing screening prior to anti-TNF or other immunosuppressive therapies. Further evaluation of the sensitivity and specificity of this novel whole-blood assay is warranted.