BACKGROUND: Interferon gamma release assay (IGRA) is an in vitro blood test to measure interferon gamma (IFN-γ) released from antigen-specific T cells after stimulation with pathogen-specific peptides. In this study, it was aimed to investigate the T-cell response using IGRA and to compare various laboratory values in Coronavirus Disease (COVID-19) patients hospitalized either in hospital inpatient departments or in intensive care units. METHODS: A total of 100 patients (50+50) who were identified as positive for COVID-19 through the molecular method in Selcuk University Faculty of Medicine Infectious Diseases Service and Reanimation Intensive Care Unit were included in the study. IFN-γ levels in blood samples collected from patients were determined using the QuantiFERON Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV-2) (QIAGEN, Germany) kit. The patients’ gender, age, c-reactive protein (CRP), aspartate aminotransferase (AST), alanine transaminase (ALT), interleukin (IL)-6, lymphocyte count, procalcitonin, and D-dimer results were obtained from the hospital automation system. RESULTS: Thirty-eight of the IGRA test results were negative, 44 were positive and 18 were inconclusive. The age of patients with negative IGRA test results was significantly higher (p<0.001) compared to patients with positive results. There were no significant differences between patients’ IGRA test results and gender, prognosis, IL-6, lymphocyte counts, CRP, AST, and ALT values. Age, death rates, D-dimer, CRP, procalcitonin, AST and ALT values of patients hospitalized in the intensive care unit were significantly higher (p<0.001) compared to the those hospitalized in the inpatient department, while conversely, the lymphocyte values were lower (p<0.001). CONCLUSION: The relatively higher IGRA negative results in the elderly, negative and intermediate results in intensive-care patients, and low lymphocyte levels in intensive-care patients indicate that the cellular immune response is diminished and/or absent. The death rates, D-dimer, CRP, procalcitonin, AST and ALT values of the patients hospitalized in the intensive care unit were higher compared to those from the in-patient department, indicating the severity of inflammation and signaling the development of organ failure. In the light of these findings, we suggest that IGRA tests may serve as a guide in immunomodulatory therapy (Tab. 2, Fig. 2, Ref. 27). Text in PDF www.elis.sk.