PURPOSE: The diagnosis of latent tuberculosis infection (LTBI) in immunosuppressed patients is challenging. Studies have shown that interferon-gamma release assays (IGRAs) are more specific and probably more sensitive than the tuberculin skin test (TST). However, there is limited data in rheumatology patients receiving immunosuppressive therapy.
METHODS: This is a prospective study conducted at a referral rheumatology clinic. We compared TST and T-SPOT. TBÖ (an IGRA) results, including agreement analysis, in patients receiving immunosuppressive therapy.
RESULTS: We studied sixty-nine patients. Fifty-three were from countries where BCG is placed routinely. Fifty-three had rheumatoid arthritis, including ten patients on TNF-alpha antagonists. Eighteen patients were TST positive and fifteen were IGRA positive. Two patients had indeterminate IGRA results. Eight patients were both TST and IGRA positive, and forty-two patients were both TST and IGRA negative (Agreement = 74.6%; kappa = 0.32; P = 0.009). Ten out of the eighteen TST-positives were IGRA negative, and seven out of the fifteen IGRA-positives were TST negative (Discordance = 25.3%). Among eighteen non-BCG vaccinated patients, the agreement was 83.3% (kappa = 0.47; P = 0.043).
CONCLUSION: There is substantial discordance between T-SPOT. TBÖ and TST results in this patient population, possibly associated with differences in the specificity of both tests in BCG-vaccinated patients.
CLINICAL IMPLICATIONS: Some TST results may not be accurate in immunosuppressed rheumatology patients. Longitudinal studies are needed to elucidate the predictive value for LTBI of IGRA testing in this patient population.
DISCLOSURE: R Khan, Other Oxford Immunotec supplied the TSPOT. TB kits.; Product/procedure/technique that is considered research and is NOT yet approved for any purpose. TSPOT. TB is not approved in the USA for the diagnosis of latent tuberculous infection.