Do higher cut-off values for tuberculin skin test increase the specificity and diagnostic agreement with interferon gamma release assays in immunocompromised Bacillus Calmette-Guérin vaccinated patients?

Purpose: Immunocompromised patients with latent tuberculosis infection (LTBI) are at high risk of progression to active tuberculosis. Detection and treatment of LTBI in this group of patients are very important to control active tuberculosis. Tuberculin skin test (TST) and interferon gamma release assays (IGRAs) are two methods for detection of LTBI. Diagnostic agreement between two tests are poor especially in Bacillus Calmette-Guérin (BCG) vaccinated immunocompromised patients. In this study, we tried to figure out if the use of a higher cut-off for TST increases diagnostic agreement with IGRAs and TST specificity and or not.

Materials/methods: In this retrospective study, BCG vaccinated solid organ transplantation (SOT) candidates and patients scheduled for anti-tumor necrosis factor-alpha (anti- TNFα) treatment patients who underwent both TST and IGRAs between 2011 and 2017 were enrolled in the study. Diagnostic agreement between the two tests was assessed for 5, 10, 15mm cut-off values for all participants, SOT candidates and anti- TNFα treatment subgroups separately.

Results: Fifty female and 55 male total 105 patients were included. In the anti- TNFα treatment group 92.8% of the patients were receiving at least one immunosuppressive drug. For all participants kappa (κ) values were 0.303, 0.370, 0.321 respectively for 5, 10 and 15mm cut-offs. For SOT candidates κ values were 0.488, 0.422, 0.288 respectively. For anti- TNFα treatment group κ values were 0.235, 0.332, 0.275 respectively.

Conclusions: In BCG vaccinated immunocompromised patients, the agreement between TST and QFT-GIT was poor regardless of cut-off value. And increasing the cut-off does not improve agreement.