Latent Tuberculosis Infection Test Agreement in the National Health and Nutrition Examination Survey.

RATIONALE

Latent tuberculosis infection (LTBI) test discordance is poorly understood.

OBJECTIVES

To determine the frequency and predictors of tuberculin skin test (TST) and QuantiFERON-TB Gold In-Tube test (QFT) discordance in the U.S.

METHODS

We analyzed data from a representative sample of the U.S. population ages 6 years and older who participated in the 2011-2012 National Health and Nutrition Examination Survey. We determined prevalence estimates of test positivity, calculated test agreement and kappa statistics, and performed multivariable logistic regression to determine predictors of discordance.

MEASUREMENTS AND MAIN RESULTS

LTBI prevalence among the U.S. born ranged from 0.6% to 2.8%, depending on how LTBI was defined, with test agreement 97.0% and kappa 0.27 (95% confidence interval, 0.18-0.36). Prevalence among the foreign born ranged from 9.1% to 20.3%, depending on how LTBI was defined, with test agreement 81.6% and kappa 0.38 (95% confidence interval, 0.33-0.44). TST(+)/QFT(-) discordance was associated with age, male sex, black race, Mexican-American ethnicity, previous TB exposure, and past LTBI treatment in U.S.-born participants, but only with higher lymphocyte count in foreign-born participants. TST(-)/QFT(+) discordance was associated with older age, previous TB exposure, and past LTBI treatment in U.S.-born participants and with older age, male sex, and past LTBI treatment in foreign-born participants.

CONCLUSIONS

In the largest population-based sample of concurrently performed TST and QFT tests in a low tuberculosis incidence population, prevalence estimates depended heavily on how LTBI was defined and test agreement was only fair. We identified several predictors of discordance warranting further study.