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Clinical and Vaccine Immunology, March 2008, p. 425-432, Vol. 15, No. 3
1071-412X/08/$08.00+0     doi:10.1128/CVI.00398-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Reproducibility of QuantiFERON-TB Gold In-Tube Assay

Sharon Perry,^1* Luz Sanchez,¹ Shufang Yang,¹ Zubin Agarwal,¹ Philip Hurst,² and Julie Parsonnet¹

Division of Infectious Diseases and Geographic Medicine, Stanford University School of Medicine, Stanford, California,¹ Santa Clara Valley Health and Hospitals System, San Jose, California²

Received 3 September 2007/ Returned for modification 7 November 2007/ Accepted 6 January 2008

Studies are needed to characterize the reproducibility of QuantiFERON-TB Gold (QFT-G) for targeted U.S. screening populations. Members of northern California households were tested with the QFT-G in-tube assay (QFT-G-IT) at two home visits 3 months apart. Reproducibility and agreement with the tuberculin skin test (TST) were assessed. Monte Carlo simulation was used to evaluate the role of test-related error. Of 63 individuals (49 adults and 14 children) completing QFT-G-IT at both time points, 79% were foreign-born (98% from Latin America) and 68% reported Mycobacterium bovis BCG vaccination. At the baseline visit, 23 (37%) were TST positive and 15 (24%) were QFT-G-IT positive ( = 0.48 [± 0.11]). At 3 months, 3/48 (6.3%; 95% confidence interval [95CI], 2 to 17) of those initially QFT-G-IT negative converted, and 5/15 (33%; 95CI, 15 to 58) of those initially QFT-G-IT positive reverted. Among the 8 individuals with inconsistent QFT-G-IT results, the maximum gamma interferon response at either visit was 0.68 IU/ml versus means of 4.99 (± 3.74) and 6.95 (± 5.6) for 10 persistent positives at the first and second visits, respectively. Expected false-reversion and -conversion rates were 32% (90CI, 25 to 39%) and 6.95% (90CI, 4.6 to 9.8%) when the sensitivity and specificity were assumed to average 70% and 98%, respectively. Transient responses to QFT-G-IT are common, and low positive results need to be interpreted with caution. Further studies are needed to characterize the predictive value of the test for U.S. foreign-born and other targeted screening populations.

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* Corresponding author. Mailing address: Stanford University, 300 Pasteur Drive, S131 Grant Bldg., Stanford, CA 94305-5407. Phone: (415) 505-3048. Fax: (650) 725-3584. E-mail: shnperry{at}stanford.edu

Published ahead of print on 16 January 2008.

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Clinical and Vaccine Immunology, March 2008, p. 425-432, Vol. 15, No. 3
1071-412X/08/$08.00+0     doi:10.1128/CVI.00398-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

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