Reasons for requesting an interferon gamma release test from internal medicine and rheumatology clinics and evaluation of the results

Abstract

Background/Aim: Tuberculosis is a disease involving many systems, such as the lung, gastrointestinal system, genitourinary system, etc. Detecting this disease in its latency significantly reduces the morbidity and mortality associated with tuberculosis. One of the tests used in latent TB screening is the interferon gamma release test. In rheumatology practices, it is routinely used to screen for latent tuberculosis infections before treatment with biological agents and Janus kinase (JAK) inhibitors, and it can also be used to exclude tuberculosis infection in clinical practice. In our study, we aimed to evaluate the reasons for requesting interferon gamma release tests and the results of this test in patients who requested it. Methods: Patients admitted to internal medicine and rheumatology outpatient clinics were retrospectively screened within the retrospective cohort study. In total, 364 patients who requested interferon gamma release testing were included in the study. Nine patients with unclear test results were excluded. Laboratory results, demographic data, reasons for requesting the interferon gamma release test, and results were evaluated. Results: The interferon gamma release test was requested by 355 patients. Of these, 266 patients (74.9%) asked for latent tuberculosis screening before treatment with biological agents and JAK inhibitors. This was followed by patients with peripheral lymphadenopathy-lung nodules, patients with unexplained elevated acute phase reactants, and patients with constitutional symptoms, respectively. Ten out of 107 patients (9.3%) had an active tuberculosis infection, while six out of ten patients (60%) had pulmonary tuberculosis, and four (40%) had extrapulmonary tuberculosis. Conclusion: The most common reason for requesting the interferon gamma release test in internal medicine and rheumatology clinics was screening for latent tuberculosis before treatment with biologic agents and JAK inhibitors. In internal medicine, it has been observed that this test can also be requested by patients with constitutional symptoms, unexplained elevated acute phase reactants, and a preliminary diagnosis of tuberculosis in order to rule out or strengthen the preliminary diagnosis.