ABSTRACT
Introduction/Aim: The interferon gamma release assay (IGRA), used in diagnosing latent tuberculosis infections (LTBI), relies on the release of interferon gamma from T-cells exposed to M. tuberculosis specific peptides. An 'indeterminate' IGRA result is most commonly due an inadequate control (or 'mitogen') response, which may reflect underlying T-cell dysfunction, that is potentially associated with markers of severity in patients with COVID-19. The aim of this study was to determine associations and predictors of an indeterminate IGRA in hospitalised patients with COVID-19. Method(s): We performed a single centre, retrospective study on COVID-19 patients admitted to a tertiary referral hospital who had IGRA testing performed over a 5 months period. Demographics, markers of COVID-19 severity and other parameters were recorded, along with outcomes of COVID-19 infection. The primary outcomes included predictors of indeterminate IGRA results and associations with COVID-19 outcomes (severity, length of stay and mortality). Result(s): A total of 181 patients were included for analysis. Outcomes of IGRA testing included negative (n = 117) and indeterminate (n = 60) results. Patients with a positive IGRA (n = 4) were excluded from analysis. The odds of an indeterminate IGRA were increased with a higher severity grade of COVID-19 (OR 2.5;95% CI 1.3-4.9), immunosuppression at baseline (OR 2.3;95% CI 1.1-4.7) and when IGRA testing was done after immunosuppression for COVID-19 was commenced (OR 1.4;95% CI 1.1-1.8). A longer length of stay was more likely with an indeterminate IGRA compared to a negative result (OR 1.08;95% CI 1.03-1.14), No difference in mortality between the two IGRA subgroups was found. Conclusion(s): Our study demonstrates an indeterminate IGRA was associated with markers of disease severity and immunosuppression. In this cohort an indeterminate result was also associated with worse COVID-19 outcomes in hospitalised patients. This result could potentially be used as a prognostic marker for patients admitted with COVID-19.