Clinical significance of an equivocal interferon γ release assay result.

Abstract

To identify clinical risk factors for obtaining an 'equivocal' T-SPOT.TB result in patients consistent with tuberculosis (TB)-associated uveitis (TAU). Prospective cohort study of consecutive new patients, with ocular signs consistent with TAU at a single tertiary centre enrolled over 15 months. All subjects underwent ocular and systemic evaluation, and investigations to rule out underlying disease. Subjects with underlying disease and interdeterminate T-SPOT.TB results were excluded. Patients were followed up for 1 year from enrolment. 15 of 155 subjects (9.67%) obtained 'equivocal' T-SPOT.TB results. Mean age was 52.2 (range 12-77) years. Most of the subjects were Chinese (n=8, 53.3%) with no sex dominance (seven male, eight female). None were immunocompromised. Patients aged <13 or >55 years old were found to be more likely to have an 'equivocal' T-SPOT.TB result (OR 21.2; 95% CI 3.7 to 121.6; p=0.001), while adjusting for possible confounders including sex, race, history of diabetes mellitus, disease duration, type of uveitis and tuberculin skin test positivity. These patients are more likely to be QuantiFERON-TB Gold In-tube negative (OR 14.7; 95% CI 1.2 to 179.9; p=0.035). An 'equivocal' T-SPOT.TB result is associated with patients aged >55 years. Such patients are likely to have a negative QuantiFERON-TB Gold In-tube result.