Tuberculin skin test before biologic and targeted therapies: does the same rule apply for all?

Abstract

Background: Several societies published recommendations for latent tuberculosis infection (LTBI) screening before biological and targeted synthetic diseasemodifying anti-rheumatic drugs (DMARDs) in rheumatoid arthritis (RA) but not for other in ammatory arthritides such as spondyloarthritis (SpA). Using RA guidelines could result in overestimating Tuberculin Skin Test (TST) positivity in SpA. This study aimed to compare the distribution of TST results in SpA and RA patients along with comparison in terms of QuantiFERON®-TB Gold In-Tube (QFT-GIT) test in a Bacillus Calmette-Guérin-vaccinated population.Methods: Adult RA (n=206) and SpA (n=392) patients from the TReasure database who had both TST and QFT-GIT prior to initiation of biological and targeted synthetic DMARDs were included in the study. Demographic and disease characteristics along with pre-biologic DMARD and steroid use were recorded. The distribution of TST and performance with respect to QFT-GIT were compared between RA and SpA groups.Results: Pre-biologic conventional DMARD and steroid use was higher in the RA group. TST positivity rates were 44.2% in RA and 69.1% in SpA for a 5 mm cutoff (p<0.001). QFT-GIT positivity was slighlty higher in the SpA group (15% vs 8.9%, p=0.075). QFT-GIT positivity and disease category independently predicted a 5 mm or higher TST. The two tests poorly agreed in both groups at a TST cut-off of 5 mm (κ<0.1 for both groups). Increasing the TST cut-off only slightly increased the agreement between the two tests.Conclusions: TST positivity was more pronounced in SpA compared to that in RA and this was not explainable by pre-biologic DMARD and steroid use. The agreement of TST with QFT-GIT was poor in both groups. Using a 5 mm TST cut-off for both diseases could result in overestimating LTBI in SpA.