Agreement of IFN-gamma release assay and skin test in diagnosis of latent tuberculosis infection

Considering the fact that more than one third of the world’s population is infected with Mycobacterium tuberculosis bacteria, identifying individuals with latent tuberculosis infection (LTBI) is vital for controlling TB. Tuberculin skin test (TST) and IFN-gamma release assays are practical methods used for screening people with LTBI. Due to the insufficiency of data on endemic tuberculosis region and the need for evaluation of these methods in a high-risk population, this study was performed in Zahedan. This descriptive study was carried out on 75 individuals, including 21 health care workers (HCWs) as well as 54 family members of patients with active TB. IFN-γ release assay and TST were also carried out on the participants. Of the 75 participants, 26 had positive IFN-γ release assay results and 49 persons showed negative results. TST was also performed and 12 participants did not show up for taking the results. Among the remaining 63 participants, 60.31% had more than 10 mm indurations. The results in 32.25% of the participants were positive for both IFN-gamma release assay and skin test, whereas 34.92% of the participantspresented negativetestrresultsfor both IFN-gamma release assay and skin test. The agreement between these two tests was 66.67 % (P=0.001, K=0.36, 95% Confidence Interval). The results showed a weak agreement between the two tests.