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Madeline Slater, Anthony DuBose, Niaz Banaei, False-Positive Quantiferon Results at a Large Healthcare Institution, Clinical Infectious Diseases, Volume 58, Issue 11, 1 June 2014, Pages 1641–1642, https://doi.org/10.1093/cid/ciu139
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To theEditor—Eighteen million US healthcare workers (HCWs) undergo mandatory annual screening for latent tuberculosis [1]. Screening is also performed in tuberculosis contacts, immunocompromised patients, and other individuals employed in the public sector. Many institutions have switched from the tuberculin skin test to the Quantiferon (QFT) assay for latent tuberculosis screening. In recent months, we experienced a sharp increase in false-positive QFT results. We want to ensure that other institutions using QFT testing are aware of the potential problem of false-positive results.
Our institution began using the QFT test in 2008, screening approximately 10 000 HCWs annually. Due to the detection of transient increases in the daily positivity rate, the clinical laboratory implemented a surveillance program in 2010 for tracking daily positivity rates. As we have reported previously [2], in November 2011, the proportion of positive results significantly increased, from a mean baseline of 9% to a mean of 31%. The elevated proportion of positive QFTs returned to baseline after switching to a new lot of tuberculosis antigen tubes. Direct comparison of the tubes with tubes from a different lot identified that a lot-specific problem with the tuberculosis antigen tubes was the root cause of false-positive results. The manufacturer reportedly instituted stricter quality assurance measures prior to distribution of the QFT assays.
