[Evaluation of QuantiFERON®-TB Gold in Tube Test and Tuberculin Skin Test in the diagnosis of Mycobacterium tuberculosis infection]

Abstract

The aims of this study were to evaluate the sensitivity of QuantiFERON®-TB Gold in Tube (QFT) test and its agreement with the tuberculin skin test (TST), to investigate possible factors associated with indeterminate QFT test results and to explore the relationship between latent tuberculosis infection (LTBE) prevalence and the rate of tuberculosis (TB) cases in our region. 1455 cases with QFT test performed in Ege University Faculty of Medicine Hospital between 2013 and 2015 were included in the study and simultaneously TST results of 268 of 1455 cases were reached. TST results were evaluated according to both ≥ 10 mm and ≥ 15 mm cut-off values. The QFT results of the cases were compared according to their gender, age groups and clinical characteristics with chi-square test. Stratified analyses were also conducted according to age groups. Multivariate logistic regression was used to analyse factors associated with QFT positivity and indeterminate QFT results. Cohen's kappa was used to test the agreement between QFT and TDT, overall and stratified according to age groups. Among 1455 cases, 396 (27.2%) were QFT positive and 120 (8.2%) had an indeterminate QFT result. When the indeterminate results were excluded, QFT positivity was found as 29.7%. The highest indeterminate results were determined among 0-4 year-old and ≥ 65 year-old groups as 17.6% and 12.1%, respectively and lowest among the 55-64 age group as 4%. The comparison of the cases without any cellular immunity defect and the patients with hematologic malignancies or immune deficiency and patients under immunosuppressive treatment had two and 2.44 times more indeterminate QFT results, respectively. Among 268 cases with TST results reached, QFT positivity was 30.6%; 38.1% for TST ≥ 10 mm and 25.7% for TST ≥ 15. After the exclusion of indeterminate results, the agreement between QFT and TST ≥ 10 mm was 71.3% for positive cases and 75.5% for negative cases. The highest agreement between QFT and TST ≥ 10 mm was in the age group 35-64 and lowest in the age group ≥ 65. Among 43 culture-positive cases, 32 had QFT positive, six negative and five indeterminate results. When indeterminate results were excluded, the sensitivity of thetest was 84.2% (32/38) among culture-positive active TB cases. TST results were available for 17 of the culture-positive cases, among them QFT sensitivity was 76.5% (13/17), TST sensitivity 70.6% (12/17) and the sensitivity of both tests was 88.2% (15/17). The ratio of QFT positivity has increased as the age increased. Interestingly, QFT positivity was higher among females than males in the 15-34 age group and higher among males in the 35-64 age group. The rates of QFT positivity were lower among immunocompromised patients. When QFT and TST positivities were compared with the rate of TB cases among age groups, QFT positivity was observed as parallel to the rate of TB cases. In conclusion, although the sensitivity of QFT was higher than TST, it was found that it could not be considered as a gold standard in LTBE diagnosis. As active TB cases originate from the LTBE pool, QFT test results might be considered a better indicator of active TB development risk.