Comparison of t-spot.tb and tuberculin skin test in latent tuberculosis infection and active tuberculosis disease

The diagnosis of latent tuberculosis infection relies on the tuberculin skin test that has many drawbacks. The specifity of tuberculin skin test is poor because of cross-reactivity with M. bovis BCG vaccine and environmental mycobacteria. The aim of this study was to evaluate the reliability of the tuberculin skin test and the interferon-gamma enzyme-linked immunospot assay (T-SPOT.TB) in tuberculosis patients and health care workers with known exposure to M. tuberculosis and healthy volunteers with no known tuberculosis contact. We also investigated whether a rapid diagnosis of active pulmonary tuberculosis can be established by enumeration of M. tuberculosis- specific T lymphocytes from induced sputum in routine clinical practice. We conducted a prospective study enrolling a total of 91 participants with newly diagnosed culture-proven tuberculosis patients (n=31) and health care workers with known exposure to M. tuberculosis (n=30) and healthy volunteers with no history of tuberculosis and no known tuberculosis contact (n=30) in a BCG vaccinated study population. The sensitivities of the T-SPOT.TB and tuberculin skin test were 79,3 % and 25,8%, while their specifities were 75,9% and 56,7%, respectively. Negative predictive value and positive predictive values of T-SPOT.TB were 78,6%, 76,7%; and negative predictive value and positive predictive values of tuberculin skin test were 42,5%, 38,1%, respectively. 26,7% of the tuberculosis contacts were positive by T-SPOT.TB test, and 60% by tuberculin skin test. Induced sputum T-SPOT.TB test results were undefined in 72,6% of active tuberculosis patients. The sensitivity of the T-SPOT.TB assay is greater than that of tuberculin skin test. T-SPOT.TB test allows a more rapid exclusion of tuberculosis in suspected cases than tuberculin skin test. T-SPOT.TB offers a more accurate approach than tuberculin skin test for identification of individuals who have latent tuberculosis infection.