Interferon gamma release assay compared with the tuberculin skin test for latent tuberculosis detection in pregnancy.

OBJECTIVE

To estimate agreement and correlation between the tuberculin skin test and an interferon gamma release assay for detecting latent tuberculosis (TB) infection in pregnant women.

METHODS

We conducted a cross-sectional study of pregnant women initiating prenatal care at a university-affiliated public hospital between January 5, 2009, and March 15, 2010. Eligible women received a questionnaire about TB history and risk factors as well as the tuberculin skin test and phlebotomy for the interferon gamma release assay. Agreement and correlation between tests were estimated, and different cutoffs for interferon gamma release assay positivity were used to assess effect on agreement. Furthermore, predictors of test positivity and test discordance were evaluated using multivariable analysis.

RESULTS

Of the 220 enrolled women, 199 (90.5%) returned for tuberculin skin test evaluation. Over 70% were Hispanic and 65% were born in a country with high TB prevalence. Agreement between the tuberculin skin test and interferon gamma release assay was 77.39 (κ=0.26). This agreement was not significantly changed using different cutoffs for the assay. Birth bacille Calmette-Guérin vaccination was associated with tuberculin skin test positivity (odds ratio [OR] 4.33, 95% confidence interval [CI] 1.4-13.48, P=.01), but not interferon gamma release assay positivity. There were no statistically significant predictors of the tuberculin skin test and interferon gamma release assay result discordance; however, birth in a high-prevalence country was marginally associated with tuberculin skin test-positive and interferon gamma release assay-negative results (OR 2.94, 95% CI 0.86-9.97 P=.08).

CONCLUSION

Comparing the tuberculin skin test and interferon gamma release assay results in pregnancy, concordance and agreement were poor. Given that much is still unknown about the performance of interferon gamma release assays in pregnancy, further research is necessary before the tuberculin skin test is abandoned for screening of latent TB infection in pregnancy.

LEVEL OF EVIDENCE: III.