New tests for latent TB may be unreliable in pregnancy
A new report warns against using interferon gamma release assays (IGRA) to look for tuberculosis in pregnant women
More research is needed "before the tuberculin skin test is abandoned for screening of latent TB infection in pregnancy," the authors say.
"There was poor correlation between the traditional tuberculin skin test and the IGRA in detecting latent TB infection. This could represent either a false positive skin test or a false negative IGRA in pregnant women," senior author Dr. Deborah Cohan of the University of California, San Francisco told Reuters Health by email.
"While there is concern about false positive skin testing," she added, "especially among those who received BCG vaccination as a child, our study found that prior receipt of BCG vaccination didn't predict discordant results."
In Obstetrics and Gynecology this month, Dr. Cohan and colleagues report on their comparison of the two tests in 199 women. Most were Hispanic, and 65% were born in a country with a high TB prevalence.
Twenty-three percent had positive tuberculin skin tests and 14% had positive IGRA results, for a 77.4% rate of agreement. There were no statistically significant predictors of discordant results.
Birth in a high TB prevalence country was marginally associated with positive results on both tests (odds ratio, 2.94).
"Because the IGRA measures interferon gamma release and the normal immune changes in pregnancy may alter interferon gamma release, there is biological plausibility that IGRA do not function as well in pregnancy," Dr. Cohan said. "While there are logistical advantages to using IGRA instead of skin testing, we need to better understand the accuracy of this assay in pregnancy."
By David Douglas
Obstet Gynecol 2011;118:1363-1370.
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