Smoking leads to false negatives in TB test

A recent study conducted in Tanzania and Denmark found that cigarette smoking caused false negative and indeterminate interferon gamma release assay results for tuberculosis testing.

While smoking cigarettes was known to increase TB risk and to impair interferon-gamma responses to antigenic challenge, the impact of smoking on tests like the QuantiFERON-TB Gold assay was not known. Researchers tested the effects of smoking in IGRA performance in TB patients in settings with both low and high TB prevalence, BioMedCentral reports.

The researchers determined that smokers in Denmark and Tanzania had lower IFN-gamma antigen responses, fewer positive and more false negative QFT-G results. In the Tanzania patients, logistic regression analysis found that smoking was associated with false negative and indeterminate QFT results, BioMedCentral reports.

The QuantiFERON-TB Gold assay is a test that is meant to yield fewer false positive TB test results by specifically testing for Mycobacterium tuberculosis infection. The tuberculin skin test, which is more commonly used to test for TB, can cause false positives among patients previously vaccinated with the bacillus Calmette-Guerin TB vaccine.

A study published in the October edition of the Journal of Infection and Public Health found that the QFT-G assay yielded fewer false positives than the tuberculin skin test.