Reproducibility of QuantiFERON®-TB GOLD In-tube Assay

Division of Infectious Diseases and Geographic Medicine, Stanford University School of Medicine, Stanford, CA, US; Santa Clara Valley Health and Hospitals System, San Jose CA, US

^* To whom correspondence should be addressed. Email: shnperry{at}stanford.edu.

	Abstract

Background: Studies are needed to characterize reproducibility of the QuantiFERON-TB GOLD® in targeted US screening populations. Methods: Members of Northern California households were tested with the QuantiFERON-TB Gold® In-Tube assay (QFT-G-IT) at two home visits 3 months apart. Reproducibility and agreement with TST were assessed. Monte Carlo simulation was used to evaluate the role of test-related error. Results. Of 63 individuals (49 adults and 14 children) completing QFT-G-IT at both time points, 79% were foreign-born (98% Latin America) and 68% reported Bacille Calmette-Guérin (BCG) vaccination. At baseline, 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% CI: 2-17) initially QFT-G-IT negative converted, and 5/15 (33%; 9% 5CI: 15-58) initially QFT-G-IT positive reverted. Among the 8 individuals with inconsistent QFT-G-IT results, the maximum IFN- response at either visit was 0.68 IU/ml vs. a mean of 4.99 (+/- 3.74) and 6.95 (+/-5.6) in 10 persistent positives, at 1^st and 2^nd visits respectively. Expected false reversion and conversion rates were 32% (90CI, 25-39) and 6.95 (90CI, 4.6-9.8) when the sensitivity and specificity were assumed to average 70% and 98%, respectively. Conclusions: 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 in US foreign-born and other targeted screening populations.