JCM Accepts, published online ahead of print on 9 April 2008

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J. Clin. Microbiol. doi:10.1128/JCM.02403-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

SENSITIVITY COMPARISON OF TWO COMMERCIAL INTERFERON-GAMMA RELEASE ASSAYS IN PULMONARY TUBERCULOSIS

Cynthia B E Chee^*, Suay H Gan, Kyi W KhinMar, Timothy M Barkham, Chwee K Koh, Shen Liang, and Yee T Wang

Singapore Tuberculosis Control Unit, Tan Tock Seng Hospital, Singapore; Dept of Pathology and Laboratory Medicine, Tan Tock Seng Hospital, Singapore; Statistics Unit, Dean's Office, Yong Loo Lin School of Medicine, National University of Singapore

^* To whom correspondence should be addressed. Email: cynthia_chee{at}ttsh.com.sg.

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

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