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Interferon γ release assay for the diagnosis of uveitis associated with tuberculosis: a Bayesian evaluation in the absence of a gold standard
  1. Marcus Ang1,2,
  2. Wan Ling Wong2,3,
  3. Xiang Li2,4,
  4. Soon-Phaik Chee1,3
  1. 1Singapore National Eye Centre, Singapore, Singapore
  2. 2Singapore Eye Research Institute, Singapore, Singapore
  3. 3Department of Ophthalmology, Yong Yoo Lin School of Medicine, National University of Singapore, Singapore, Singapore
  4. 4Department of Statistics and Applied Probability, National University of Singapore, Singapore, Singapore
  1. Correspondence to Associate Professor Soon-Phaik Chee, Ocular Inflammation and Immunology Service, Singapore National Eye Centre, 11 Third Hospital Avenue, 11 Third Hospital Avenue, Singapore 168751, Singapore; chee.soon.phaik{at}snec.com.sg

Abstract

Aim To evaluate an interferon γ release assay in the diagnosis of uveitis associated with tuberculosis (TB), in the absence of a gold standard.

Methods We conducted a prospective 1-year study on consecutive patients with a new diagnosis of uveitis presenting with ocular signs suggestive of TB-associated uveitis (TAU). All subjects underwent ocular and systemic review with investigations, including T-SPOT.TB assay and tuberculin skin test (TST). The main outcome measures were sensitivity and specificity; positive and negative predictive values (PPV, NPV) of T-SPOT.TB were estimated using Bayesian statistics (presented with 95% Bayesian credible intervals (CrI)).

Results Analysis after exclusion of patients with indeterminate results and other diseases included 191 patients, with mean age of 47.2±15.3 years. The majority were Chinese (n=110, 57.6%) and women (n=102, 53.4%). The TST (0.70, 0.65 to 0.75) was more sensitive compared to T-SPOT.TB (0.53, 0.42 to 0.66) but the T-SPOT.TB (0.91, 0.88 to 0.93) was more specific than TST (0.71, 0.58 to 0.83). The T-SPOT.TB had a higher PPV (0.88, 0.80 to 0.93) compared to the TST (0.76, 0.57 to 0.90), but a lower NPV (0.60, 0.38 to 0.78) than the TST (0.65, 0.46 to 0.78). Patients who are TST and T-SPOT.TB positive are very likely (95.1% likelihood) to have TAU (39/41 95% CrI 35 to 41). Based on statistical decision theory, in populations where the prevalence of TAU is high the TST should be the first-choice test; the T-SPOT.TB should be performed if the prevalence of TB is low.

Conclusions The T-SPOT.TB assay is more specific but less sensitive than the TST and should be used in preference to the TST in low-TB-prevalence populations. Used in conjunction, the likelihood of TAU is greatest if the T-SPOT.TB and TST are both positive.

  • Inflammation
  • Infection
  • Diagnostic tests/Investigation

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