Optimized Cut-off Value of QuantiFERON-TB Gold Plus Test for Diagnosis of Ocular Tuberculosis in Endemic Population.

PURPOSE: To evaluate the diagnostic performance and optimal cut-off values of QuantiFERON-TB Gold Plus (QFT-Plus) for the diagnosis of ocular tuberculosis (TB) in a TB-endemic population.

METHODS

Medical records of patients who underwent QFT-Plus testing between January 2019 and December 2022 were retrospectively reviewed. Ocular TB was diagnosed according to the Collaborative Ocular Tuberculosis Study (COTS) criteria. QFT-Plus values, including TB1-Nil, TB2-Nil, and TBmax-Nil (defined as the higher value of TB1-Nil and TB2-Nil), were compared between ocular TB and non-ocular TB groups. Receiver operating characteristic (ROC) curve analysis was performed to evaluate diagnostic performance and determine optimal cut-off values. Subgroup and sensitivity analyses were conducted to assess the impact of incorporation bias and treatment response.

FINDINGS: Among 387 patients, 104 (26.9%) had positive QFT-Plus results and 85 (22.0%) were diagnosed with ocular TB. Median TB1-Nil and TB2-Nil values were significantly higher in patients with ocular TB than in those with non-ocular TB (1.49 vs 0.01 IU/mL and 1.52 vs 0.01 IU/mL, respectively; both P < 0.001). ROC analysis demonstrated favorable diagnostic performance, with AUCs of 0.926 (95% CI, 0.885-0.967) for TB1-Nil, 0.930 (95% CI, 0.890-0.971) for TB2-Nil, and 0.931 (95% CI, 0.891-0.970) for TBmax-Nil. Optimal cutoff values were 0.29 IU/mL for TB1-Nil, 0.29 IU/mL for TB2-Nil, and 0.39 IU/mL for TBmax-Nil. At the manufacturer-recommended threshold of 0.35 IU/mL, sensitivities ranged from 88.2% to 92.9% and specificities from 91.1% to 92.4%. Subgroup and sensitivity analyses yielded broadly consistent findings.

IMPLICATIONS: QFT-Plus demonstrated favorable diagnostic performance for ocular TB in this TB-endemic population. The manufacturer-recommended cut-off value of 0.35 IU/mL showed diagnostic performance comparable to the optimal thresholds identified in this study, supporting its continued use in the diagnostic evaluation of ocular TB.