Comparison of Sensitivities of Two Commercial Gamma Interferon Release Assays for Pulmonary Tuberculosis

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Abstract
There are few head-to-head comparisons of the commercial gamma interferon release assays (GIRAs). We compared the performance of the T-SPOT.TB and QuantiFERON-TB Gold In-Tube (QFT-IT) assays in patients with culture-proven pulmonary tuberculosis. Blood was drawn for both assays within 14 days of starting antituberculosis treatment. The QFT-IT indeterminate rate was 3.5%; the T-SPOT.TB failure rate was 1.4%. There was poor agreement between the GIRAs (κ = 0.257) among the 270 patients with valid results for both tests. The sensitivities of the T-SPOT.TB and QFT-IT assays were 94.1 and 83.0%, respectively, with a significant difference in the performance of the assays (P = 0.001 [McNemar test]). Factors independently associated with indeterminate QFT-IT results were an age of ≥60 years (odds ratio [OR] 11.18, 95% confidence interval [CI] = 1.841 to 67.823, P = 0.009), female sex (OR = 7.47, 95% CI = 1.517 to 36.733, P = 0.013) and non-Chinese (i.e., Indian or Malay) race (OR = 7.89, 95% CI = 1.585 to 39.267, P = 0.012). The QFT-IT assay was significantly less sensitive in patients ≥60 years old (OR = 0.41, 95% CI = 0.181 to 0.918, P = 0.030) and in Indian compared to Chinese patients (OR = 0.27, 95% CI = 0.073 to 0.990, P = 0.048). The T-SPOT.TB assay was significantly less sensitive in Malay (OR = 0.23, 95% CI = 0.063 to 0.815, P = 0.023) and Indian patients (OR = 0.09, 95% CI = 0.017 to 0.429, P = 0.003) compared to Chinese patients. The performance of both assays was not significantly altered in diabetics. The diminished sensitivity of the GIRAs in persons of Malay and Indian race merits further study.

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