Inconsistency of QuantiFERON-TB Gold Test and Tuberculin Skin Test Results in the Evaluation of Latent Tuberculosis Infection in Health Care Workers

Problem considered: Working in hospital wards, especially the infectious and pulmonary diseases wards, increases the likelihood of the risk of the health care staff with a variety of infectious factors, including the Mycobacterium tuberculosis. The present study was aimed to evaluate the QFT and TST test as well as vitamin D deficiency for screening the tuberculosis health care staff of the tuberculosis sections in Khorasan Razavi province. Methods: In this respect, 44 Tuberculosis health care staff of the tuberculosis sections in Khorasan Razavi province who are directly related to tuberculosis patients were included. TST was performed and chest radiography was done on all the subjects on the day of sampling and the results were collected. The expression of T-bet, FOXP3, and RORyt genes was evaluated by TaqMan Real-time PCR after the lymphocyte isolation by gradient Ficoll lymphocyte assay for immunological isolation and after cDNA synthesis. QFT was performed using the QFT-plus kit the day after sampling in accordance with the instructions in the kit. Results: Out of the 54 TB staff in the province, who were invited for the test, 16 personnel refused to follow the test. Out of 38 participants, TST was positive for 6 people (15.7%), and the QFT test was also positive for 10 people (26.3%), while 4 (10.5%) people showed positive results in both tests. Among 38 cases, the agreement between the two TST and QFT tests was 63% (P-value < 0.0001) among the 38 subjects. The sensitivity and specificity of the TST test were 40 and 93%, respectively as compared to those of QFT. Comparing the results of the QFT positive group to the QFT negative group, the T-bet gene expression in the QFT positive group was 130.9 and the QFT negative group was 34.06, which were statistically significant. Thus, the expression of this gene in the QFT positive group was 3.8 times higher than that of the negative QFT group. Moreover, Foxp3 gene expression in the QFT group was equivalent to 233.3, and in the negative QFT, the group was equivalent to 93.5, which was statistically significant. Therefore, the expression of this gene in the QFT positive group showed an increase 2.3 times higher than that of the negative QFT group. Conclusion: According to the results of this study, the QFT test can be an appropriate alternative for skin tests in a high-risk group for TB.