Cytokine Release Assay Favored for Latent TB in Pregnancy

The interferon-gamma release assay (IGRA) blood test for tuberculosis diagnosis is more specific in pregnant women and may be a better predictor of disease progression.

Although IGRAs are currently recommended over skin testing for pregnant women with risk factors for exposure to Mycobacterium tuberculosis, the US Centers for Disease Control and Prevention (CDC; Atlanta, GA, USA) recommendations were made without data on IGRA performance during pregnancy.

Doctors at the New York University School of Medicine (NY, USA) analyzed the performance of the IGRA blood test in 140 pregnant and 140 nonpregnant adolescents and women receiving care at public hospital outpatient clinics. About 90% had at least one risk factor for exposure to M. tuberculosis. All but three of the 103 pregnant women and adolescents who had negative Mantoux tuberculin skin test results also had negative IGRA, and the overall agreement between tuberculin skin test and IGRA results was 88% for all pregnant patients.

The IGRA kit used in the study was the QuantiFERON-TB Gold In Tube assay (Cellestis; Valencia, CA, USA). Only 12 of the 28 women (43%) with positive skin test results had positive IGRA results and five of them had received the Bacillus Calmette-Guérin (BCG) vaccine. The proportion of pregnant patients with a positive IGRA increased with the likelihood of exposure to M. tuberculosis, and no one without a known risk factor for M. tuberculosis had a positive result on either test. Interferon-gamma levels did not differ significantly during any trimester of pregnancy. None of the 25 women who underwent repeated IGRA testing during their pregnancy or postpartum converted from negative to positive or vice versa. IGRA results did not differ significantly between the pregnant and nonpregnant patients in the study.

Jennifer Lighter-Fisher, MD, a coauthor of the study, said, "IGRAs cost between USD 30 to USD 60 a test, which is much more expensive than a skin test, but the higher cost would be offset by greater efficiency. In our study, we observed less than half of the women with positive skin tests had a positive IGRA. Therefore, the additional cost of IGRAs is offset by a decrease in the number of positive test results and the associated costs of evaluating and treating tuberculin skin test-positive patients. If the IGRAs were to be used instead of the skin test during pregnancy, far fewer women will be identified as positive and therefore would have avoided a chest X-ray during pregnancy and a nine-month regimen of anti-TB medication." The study was published in the June 2012 issue of Obstetrics and Gynecology.

Related Links:
US Centers for Disease Control and Prevention
New York University School of Medicine
Cellestis