Tuberculosis Test May Underreport in Pregnant Women With HIV

Pregnancy may confound tuberculosis (TB) tests results in women with HIV, according to research published in the American Thoracic Society’s American Journal of Respiratory and Critical Care Medicine.

The study compared the accuracies of the Quantiferon Gold In Tube (QGIT) test blood test and the tuberculin skin test (TST) on a population of pregnant women. The goal of the study was to determine a method to identify those women carrying a latent TB infection, who are most likely to develop active TB. Because pregnancy and HIV compromise the immune system, this population has an increased risk of developing active TB.

“The World Health Organization and many governments endorse the TST because it is a cheap and ubiquitous test,” lead study author Jyoti Mathad, MD, MSc, Instructor of Medicine in the Center for Global Health at Weill Cornell Medical College, said in an American Thoracic Society press release. “However, our over-reliance on this single test means that we are failing to detect and treat a potentially life-threatening infection in tens of millions of high-risk women.”

The study included 252 women in their second or third trimester who received care from a public teaching hospital in India. The participants received TB testing at enrollment, during pregnancy, or at delivery. The researchers also enrolled another 39 women to be included in a longitudinal study to assess how TB test results were affected in different stages of pregnancy.

Of the 252 women who were enrolled, 28% had a positive interferon gamma release assay (IGRA) but only 10% had a positive TST (P<.005). When researchers stratified the data by pregnancy vs delivery, 20% had positive IGRA/TST discordance at each time point.

The researchers also found that QGIT positivity was almost 3 times higher than the common TST at every point tested. Dr Mathad notes that pregnant women produce lower levels of immune chemicals that many TB diagnostics look for.

 “Currently we have no way of predicting which women are most likely to get sick from the disease,” she noted in the release. “Our findings about these immune chemicals provide a starting point for developing a test that will tell us who in this already high-risk population is at greatest risk of disease and death and is in most need of treatment.”

Further research on indicators of risk could also benefit other high-risk groups including the elderly, young children, and individuals who test positive for HIV.

“Pregnant women have been excluded from all 40 trials of new TB drugs that are ongoing today,” said Dr Mathad. “Some of the caution is justified, but oftentimes, it is simply the path of least resistance. This habit—and habit is all that it is in many cases—exacts a toll on women wordwide. Pregnant women often get stuck taking longer regimens of outdated drugs due to lack of research.”

Reference

1. Mathad JS, Bhosale R, Balasubramanian U, et al. Quantitative IFN-γ, IL-2 Response and Latent Tuberculosis Test Discordance in HIV-infected Pregnant Women.Am J Respir Crit Care Med. 2016; doi: 10.1164/rccm.201508-1595OC.