Predictors of interferon-gamma release assay results and their association with COVID-19 infection outcomes.

Background: An 'indeterminate' interferon-gamma release assay (IGRA) result used in the diagnosis of latent TB infection (LTBI) is most commonly due to an inadequate control (or 'mitogen') response, which may reflect underlying T-cell dysfunction.

Methods: We performed a single-centre, retrospective study on COVID-19 patients admitted to a tertiary referral hospital who had IGRA testing conducted over a 5-month period. The primary outcomes included predictors of indeterminate IGRA results and associations with COVID-19 outcomes.

Results: A total of 181 patients were included for analysis. Approximately one-third of patients hospitalised with COVID-19 with IGRA testing performed (60/181) had an indeterminate result. The likelihood of an indeterminate IGRA was increased in patients with a history of solid organ transplant and a higher severity of COVID-19 at the time of testing. An indeterminate IGRA was associated with a higher risk of severe COVID-19 and a higher risk of admission to the ICU during admission to the hospital. No difference in mortality between the two subgroups was found.

Conclusion: Our study demonstrated that COVID-19 patients on immunosuppression had a high likelihood of an indeterminate IGRA result, which was associated with markers of disease severity and immunosuppression. In this cohort, an indeterminate result was associated with worse COVID-19 outcomes.