Reproducibility of QuantiFERON-TB gold in-tube assay.
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 (kappa = 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.
Perry
Sharon
S
Division of Infectious Diseases and Geographic Medicine, Stanford University School of Medicine, Stanford, California 94305-5407, USA. shnperry@stanford.edu
Sanchez
Luz
L
Yang
Shufang
S
Agarwal
Zubin
Z
Hurst
Philip
P
Parsonnet
Julie
J
D000328:Adult; D002648:Child; D002675:Child, Preschool; D004641:Emigration and Immigration; D005260:Female; D006801:Humans; D007118:Immunoassay; D007371:Interferon-gamma / Q000097:blood*; D008297:Male; D008403:Mass Screening / Q000379:methods; D008875:Middle Aged; D009010:Monte Carlo Method; D015995:Prevalence; D011933:Reagent Kits, Diagnostic; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism; D014374:Tuberculin Test; D014376:Tuberculosis / Q000175:diagnosis* / Q000453:epidemiology; D014481:United States / Q000453:epidemiology
D011933:Reagent Kits, Diagnostic; D007371:Interferon-gamma