Sensitivity of a new commercial enzyme-linked immunospot assay (T SPOT-TB) for diagnosis of tuberculosis in clinical practice

Diagnosis of active and latent tuberculosis (TB) remains a challenge; however, over the last few years, a new approach based on detecting Mycobacterium tuberculosis-specific T cells has shown much promise. In particular, there is substantial published evidence showing that the detection of ESAT-6- and CFP-10-specific T cells using the ex vivo enzyme-linked immunospot technique is a marked improvement over the existing tuberculin skin test. This technique, which detects gamma interferon-producing T cells, is now available as the commercial assay T SPOT-TB (Oxford Immunotec, Oxford, UK). In the present study, the usefulness of the T SPOT-TB test for diagnosis of TB in real-world clinical practice was investigated. Ninety patients of a southern German referral centre for TB with confirmed or suspected TB were randomly selected for this study. The results of the T SPOT-TB test were compared with the results of conventional diagnostic tools. The T SPOT-TB test detected 70 of 72 patients with pulmonary or extrapulmonary TB, indicating a sensitivity of 97.2% (95% confidence interval, 90.3-99.7). For 45 of these patients, tuberculin skin test (TST) results were also available. Only 40 (89%) of these 45 patients were positive in the TST compared to all 45 (100%) in the T SPOT-TB test (p=0.056). Among 12 of 90 patients for whom active TB disease was ruled out, the T SPOT-TB test was negative for 11 (92%), allowing the rapid exclusion of TB in patients suspected to have active TB disease. The T SPOT-TB test is a sensitive assay for detection of TB and represents a useful addition to the diagnostic algorithm available for detecting TB in low-incidence settings.