Season Is Associated with Interferon Gamma Measured in QuantiFERON Gold In-Tube Test

BACKGROUND: The QuantiFERON Gold-in-tube (QFT) test is an Interferon Gamma Release Assay (IGRA) used to indirectly diagnose tuberculosis infection (TBI). The QFT measures Interferon gamma (INF-γ) released in response to specific Mycobacterium tuberculosis (Mtb) antigens. The main objective of this analysis is to determine whether there is a seasonal variation of the IFN-γ level released in QFT blood samples. METHODS: Data of the QFT assays conducted in health care workers (HCW) at Houston Methodist Hospital (HMH; Houston, TX) between August 2008 and April 2017 were analyzed and stratified by the season when the blood samples were drawn. Multivariate generalized linear models (GLM) controlling for age, gender and ethnicity were used to estimate IFN-γ measured in the nil and mitogen controls per season. RESULTS: Data from 10,089 QFT assays were included in the analysis. The tested HCW were primarily between the ages of 18 to 49 years (76.5%), female (65.9%), and non-Hispanic (77.0%). A significantly higher level of IFN-γ was found in the mitogen stimulated blood (Phytohemaglutinin) in the summer (June – August) (estimate: 0.19 IU/mL; P <0.001) compared with the other season, and a significantly lower level of IFN-γ was found in the fall (September – November) (estimate: -0.27 IU/mL; P <0.001) compared with the other seasons. The IFN-γ level was significantly lower in unstimulated blood (estimate: −0.02 IU/mL; P = 0.038) but not in the antigen stimulated blood samples drawn in the winter (December–February) compared with those drawn in other seasons. CONCLUSION: We observed a seasonal variation of the IFN-γ level measured in unstimulated and antigen-stimulated blood samples drawn for the QFT assays, in which seasonal factors such as airborne antigens like pollen may play a role. Clinicians should take into account the possible seasonal variation when interpreting positive QFT results, especially those on the borderline of the assay’s diagnostic cutoffs. Re-testing or implementing additional diagnostic tools should be considered if necessary. Further research would be needed to identify the specific seasonal factors that may influence the QFT results. DISCLOSURES: All authors: No reported disclosures.