A-170 Investigation of High Rate of Low Positive Quantiferon-TB Gold Plus Results

Abstract

Abstract Background Tuberculosis (TB) is a communicable disease, transmitted almost exclusively by cough aerosols carrying pathogens of the M. tuberculosis complex. TB continues to be a major public health threat, causing an estimated 10.4 million new cases and 1.3 million deaths from TB globally in 2016. Many more people may have latent tuberculosis infection (LTBI), which may go undetected without further laboratory investigation. The Quantiferon-TB Gold Plus (QFT-Plus) is an Interferon Gamma Release Assay (IGRA) for the identification of LTBI. It detects the cellular immune response to antigens of M. tuberculosis and represents an indirect marker of M. tuberculosis exposure. In January of 2021, the NorthShore University HealthSystem Core Laboratory transitioned from a reference laboratory ELISA-based QFT-Plus test to an in-house DiaSorin LIAISON® QuantiFERON®-TB Gold Plus test. After implementation, we noticed a higher rate of low positive QFT-Plus results (1.3%–5.4%) in our patient population that we regard as a mixed risk population. The expected percent of low positive results in a mixed risk population is 2%–3%. Objective To determine the potential causes of a higher rate of low positive Quantiferon-TB Gold Plus Results. Methods Forty specimens with Antigen-Nil results between 0.35–1.00 IU/mL using LIAISON® QuantiFERON®-TB Gold Plus reagent from 8/2022–10/2022 were collected for this study. All forty specimens were re-tested using ELISA-based methodology. Patient demographics and medical history were reviewed for any factor that may be responsible for the low positive results. Results Results from the two different methodologies were compared: 28/40 (70%) specimens showed positive results on the DiaSorin LIAISON®-XL platform, but negative results on the ELISA platform. Review of medical history showed that 92% of the sample population had received more than 2 doses of COVID-19 vaccine and 12.5 % had previous COVID-19 infection. 30% had an underlying autoimmune disease, with psoriasis and rheumatoid arthritis being the most common. However, no correlation was found between medical or vaccination history and the QFT-Plus results. Conclusion LIAISON® QuantiFERON®-TB Gold Plus is a Chemiluminescence immunoassay which is more sensitive than ELISA, resulting in an increased number of low positive QFT-Plus results. Physicians need to correlate clinical findings and TB exposure history to the QFT-Plus results when making clinical decisions.