Spot on! evaluation of T-spot.TB following indeterminant quantiferon TB-gold plus in screening for latent tuberculosis

Abstract

Background: Current guidelines recommend screening for latent tuberculosis in at risk patients, including immunosuppressed patients, particularly those receiving anti-TNF-alpha therapy.1 Interferon-gamma release assays (IGRA), including T-SPOT.TB (TS) and QuantiFERON TB-Gold Plus (QFG), are one method for case identification. Our lab suggests requesting TS after indeterminant QFG, although evidence for this approach is limited.1 Methods: A retrospective audit of TS tests from November 2018 to October 2019 was performed to identify the results of testing after indeterminate QFG. Additional details, including QFG mitogen response, source of referral, and interval between QFG and TS, were also examined. Result(s): Eighty TS tests with a history of indeterminant QFG result were identified. Seventy-two (90%) had a clear result, with the majority being negative (69 tests, 86%) and three positive results (3.8%). Of the remaining requests four (5%) were not performed due to low cell counts, three (3.8%) had an indeterminant result, and one (1.8%) was uninterpretable due to high background. Discussion(s): Our current strategy utilising a second IGRA (TS) after indeterminant QFG led to clarification of indeterminant results in the vast majority (90%) of cases. This outcome supports continuing our testing strategy and provides some evidence to inform changes to guidelines. Reference 1. Bastian I, Coulter C, National Tuberculosis Advisory Committee. Position statement on interferon-gamma release assays for the detection of latent tuberculosis infection. Commun Dis Intell 2017; 41: E322-36. Copyright © 2020