| Abstrakt: |
Tuberculin skin test (TST) has been used effectively for a long time, despite inherent sensitivity and specificity limitations. Patients with a positive TST without active tuberculosis are identified as having latent tuberculosis infection. Identifying patients with latent tuberculosis infection with this test is an important part of control of the disease. A whole-blood inferferon gamma (IFN-γ) assay, the Quantiferon TB Gold test (QTG; Cellestis, Australia) which is a promising in vitro diagnostic test for the identification of latent tuberculosis infection (LTBI), has potential advantages over the TST. This test includes Myobacterium tuberculosis specific ESAT- 6 and CFP-10 antigens. The aim of this study was to compare the results obtained by QTG and TST in active tuberculosis (TB) patients, close contacts of patients, health care workers and tuberculosis laboratory personel. Twenty-six patients with active pulmonary TB, 6 close contacts of those patients, 11 health care workers with contact to TB patients and 8 TB reference laboratory personnel were included in the study. Prior to administration of the TST, blood samples were drawn from each participant for QTG test. All subjects were asked for BCG vaccination history and examined for a BCG scar. All individuals had a BCG scar. The QTG assay was performed in whole blood samples according to manufacturer's instructions. The agreement between TST and QTG was measured with kappa statistical analysis. In active TB patients (true-infected cases) TST (PPD) positivity was found 34.6% (9/26) while QTG positivity was 65.3% (17/26). Although the positivity rate was higher in QTG test, this difference was not found statistically significant (p > 0.001). TST and QTG positivity rates for health care workers, close house contact of TB patients and TB laboratory staff were as follows, respectively; 36% (4/11) and 27% (3/11); 16.6% (1/6) and 83% (5/6); 37.5% (3/8) and 75% (6/8). The mean PPD diameter was 11 mm in QTG negative group and 14 mm in QTG positive group with a statistically significant difference (p < 0.001). However, there was no statistical significance between QTG positive and negative groups by means of age (p ≥ 0.05) and gender (p < 0.001). In conclusion, QTG assay was superior to TST in its ability to detect LTBI and active TB infection, not to be affected with BCG vaccination, to discriminate responses due to non-tuberculous mycobacteria, and to avoid variability and subjectivity associated with application and reading the TST. Besides, QTG assay needs only one visit to the test unit. However, its being expensive than TST and requirement for special equipments and skilled laboratory personnel, are among the disadvantages of QTG assay. |
