Background Biologic therapies have led to a dramatic change in the management of rheumatologic diseases. Although biologic agents provide profound clinical benefits, various adverse events are associated with their use particularly an increased risk of the reactivation of latent tuberculosis. Therefore, screening for latent tuberculosis infection (LTBI) is imperative before initiating biologic agents¹. Although tuberculin skin test (TST) is the most common test for detecting LTBI, Bacillus Calmette-Gue'rin (BCG) vaccination and non-tuberculosis Mycobacterium infections, can lead to false positive TST results. Interferon-gamma release assay (IGRA) measures the immune response to tuberculosis specific antigens that do not cross react with BCG, and therefore, do not cause false positive reactions in BCG recipients. Its positiveness indicates the presence of tuberculosis infection either latent or active².

Objectives We aimed to prevent the unnecessary anti-tuberculosis prophylaxis in patients whom biologic therapy is planned by evaluating the concordance between the TST and IGRA.

Methods Patients who have been receiving biologic therapy due to chronic inflammatory arthritis were enrolled in this study. Demographic and clinical data, TST and IGRA results were recorded. The agreement between IGRA and TST results was evaluated by Kappa coefficient.

Results A total of 35 patients were included; 15 (42.8%) were male and mean age was 43.74±12.72 years. Of the 22 TST positive patients, 13 (37.1%) were IGRA negative. Of the 13 TST negative patients, 3 (8.6%) were IGRA positive. Nine (25.7%) patients were positive for either of the two tests and 10 (28.6%) patients were negative for both tests. There was statistically significant discordance between two tests (p:0.021; p<0.05) (Table 1). While positive rate of TST was 62.9%, positive rate of IGRA was 34.3% and Kappa consistency coefficient between two tests was 15.4% (p:0.283; p>0.05).

Conclusions It is very common in rheumatology practice to administer anti-tuberculosis prophylaxis according to the TST. IGRA may reduce the number of patients in whom tuberculostatics are prescribed, especially in BCG recipients in endemic populations, resulting in a benefit of avoiding possible side effects. Furthermore, IGRA is also important for detecting the cases of LTBI that would be missed by TST. Confirmation in larger studies is necessary.

References

1. Costantino F, de Carvalho Bittencourt M, Rat AC, et al. Screening for latent tuberculosis infection in patients with chronic inflammatory arthritis: discrepancies between tuberculin skin test and interferon-γ release assay results. J Rheumatol. 2013 Dec;40(12):1986–93.

2. Ruan Q, Zhang S, Ai J, et al. Screening of latent tuberculosis infection by interferon-γ release assays in rheumatic patients: a systemic review and meta-analysis. Clin Rheumatol. 2016 Feb;35(2):417–25.

References

Disclosure of Interest None declared