Latent TB testing, positivity increased throughout 2021
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WASHINGTON — Data collected between 2019 and 2021 assessing trends in latent tuberculosis testing and positivity showed increased rates correlating with COVID-19 testing, researchers said at ASM Microbe.
In recent years, Labcorp frequently used the QuantiFERON-TB Gold Plus (QFT-Plus) assay to screen for latent TB. Between September 2018 and November 2021, it completed more than 5.4 million QFT-Plus tests in eight regional laboratories. In March 2021, Labcorp switched to DiaSorin LIAISON QFT-Plus reagents.
During this time, there was an increase in test positivity, prompting an investigation, according to Kristen L. Smith, PhD, a laboratory director at ViroMed Laboratories.
Smith and colleagues found that QFT-Plus positivity rates declined overall in all but one lab between September 2018 and January 2021. Data showed that in the beginning of 2021, positivity rates increased from an average of 3.92% in January to 5.79% in November, peaking at 6.77% in September.
The team reviewed the specialties ordering QFT-Plus tests and found that test positivity was higher in internal medicine and family practice (approximately 5% to 8.5%) compared with dermatology and pediatric practices (approximately 2% to 4%). Rates across the individual specialties increased in early January, with internal medicine, family practice and hospital/hospital labor increasing in positivity more drastically than pediatrics and dermatology.
The overall positivity of QFT-Plus was then compared with the overall positivity of COVID-19 PCR and antibody testing. According to the study, researchers found that positive tests for both increased in January, which they said was “consistent with the vaccination effort in the U.S. and COVID-19” antibody screening, and that the positivity trends of QFT and COVID-19 were similar.
Based on the results of the analyses, the researchers ruled out a change in tests used as the cause for an increase in positivity, while also identifying a correlation between QFT and COVID-19 positivity.
“Further investigation into the impact of COVID-19 vaccination and/or infection could help elucidate the correlation between QuantiFERON and COVID antibody positivity at Labcorp,” Smith said. “Clinical guidance would be beneficial to help clinicians navigate positive results near the cut-off because they may not be indicative of latent tuberculosis.”
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