Comparison of Tuberculin Skin Test (TST) and T-SPOT.TB Tests for Diagnosis of Latent Tuberculosis Infection (LTBI) in HIV-infected Patients

Tuberculosis (TB) is the most common opportunistic infection in human immunodeficiency virus (HIV)-infected patients. Diagnosis and treatment of latent tuberculosis infection (LTBI) is the most important step in preventing the development of active TB. In our country where TB is moderately endemic, HIV-infected patients should be investigated for LTBI. Tuberculin skin test (TST) and interferongamma release assays (IGRA) are used in the diagnosis of LTBI but there isn't a standard practice. The aim of this study is to compare the TST and T-SPOT.TB test efficiency in the diagnosis of LTBI in HIV-infected patients. Patients who had no previous active TB infection, who were not treated for LTBI and who had no active tuberculosis infection at the time of admission were included in the study. A total of 100 HIV-infected patients who were admitted to the Infectious Diseases and Clinical Microbiology out-patient clinic between June 2015 and March 2016 were evaluated cross-sectionally. CD4+ T lymphocyte counts in the last one month were detected. All patients underwent chest radiography at the time of admission. Patients who are not considered as active TB infection with clinical and laboratory findings and who had no TST within the last one month were included in the study. TST was performed after the blood samples were taken for T-SPOT.TB test. In our study, 87% of the patients were male and the mean age was 40.2. The mean CD4+ T lymphocyte count was 605 cells/mm(3) (26-1313). 16% of the patients had a history of encountring a person with tuberculosis and 81% had BCG vaccination scar. TST positivity and T-SPOT.TB positivity were 22.9% and 22%, respectively. The concordance between the two tests was found to be moderate (Kappa= 0.491). It was determined that BCG vaccination and the presence of a contact with a patient with TB did not affect TST and T-SPOT.TB test positivity (p> 0.05). There was a positive correlation between CD4+ T lymphocyte count and TST measurement values (r= 0.3, p= 0.003). Accordingly, as the number of CD4+ T lymphocytes increased, TST positivity increased (p= 0.007). T-SPOT.TB test was not affected by CD4+ T lymphocyte count (p= 0.289). Our study showed that TST was affected by CD4+ T lymphocyte count and patients' compliance with this test was also low. On the contrary T-SPOT.TB test was not affected by CD4+ T lymphocyte count. There was no statistically significant difference between T-SPOT.TB test positivity and CD4+ T lymphocyte count (p= 0.289). The concordance between the two tests was found to be moderate. It is thought that the main reason for the discordance between the tests is due to false negative or false positive results of TST. In conclusion, T-SPOT.TB was found more reliable in the diagnosis of LTBI in HIV-infected individuals. In the light of these findings, especially in HIV-infected patients with low CD4+ T lymphocyte counts, T-SPOT.TB test can be considered for LTBI diagnosis.