The prevalence of latent tuberculosis infection among Iranian sarcoidosis patients

Abstract

Background: Sarcoidosis is a multisystemic disorder with unknown causes. Mycobacterium tuberculosis has been implicated as one of the possible causes of sarcoidosis. Interferon-gamma release assays are in vitro diagnostic tests for detection of the latent tuberculosis infection (LTBI) which has been replaced by tuberculin skin test (TST) in some countries. The purpose of this study was to investigate the prevalence of LTBI in Iranian sarcoidosis patients. Methods: Ninety participants with the mean age of 42.22 ± 14.55 were enrolled in this study. They were divided into three equal groups consisted of patients with active TB, patients with sarcoidosis, and controls. TST and QuantiFERON®-TB Gold (QFT) were performed according to the manufacturer's instructions and the result interpreted. Results: The positive rates of TST were 76.66%, 3.3%, and 6.66% in TB, sarcoidosis, and control groups, respectively. However, QFT was positive in 24 (96.66%) of the TB group, 6 (20%) of sarcoidosis patients, and 5 (16.66%) of the control group. The agreement between the aforementioned tests was low (Cohen's kappa coefficient (κ) = 0.24). Conclusions: The current study suggests that in an intermediate-incidence TB population such as Iran, QFT is much more accurate than TST for the diagnosis of LTBI in patients with sarcoidosis. The present finding increases the possibility of this hypothesis which states that nontuberculous mycobacteria may play a role in the etiology of sarcoidosis.