Diagnostic usefulness of a T cell-based assay for latent tuberculosis infection in kidney transplant candidates before transplantation.

BACKGROUND: The presence of latent tuberculosis (TB) infection (LTBI) should be evaluated before kidney transplantation. Although a new T cell-based assay for diagnosing LTBI gave promising results, this assay has not yet been compared with the tuberculin skin test (TST) for diagnosing LTBI in renal transplant candidates before transplantation. PATIENTS AND METHODS: All adult patients admitted to a single institute for renal transplantation over a 1-year period were prospectively enrolled. A clinically predictive risk of LTBI was defined as: (i) recent close contact with a person with pulmonary TB; (ii) abnormal chest radiography; (iii) a history of untreated or inadequately treated TB; or (iv) a new infection (i.e., a recent conversion of TST). RESULTS: Of 209 renal recipients, 47 (22%) had a positive TST> or =5 mm, 21 (10%) had a positive TST> or =10 mm, 65 (30%) had a positive T-SPOT.TB test, and 25 (12%) had an indeterminate T-SPOT.TB test. The induration size of TST was significantly associated with a high positivity rate on T-SPOT.TB (P<0.001). Agreement between T-SPOT.TB test and TST> or =10 mm was fair (k=0.24, 95% confidence interval 0.11-0.36). However, neither univariate nor multivariate analysis showed any association between the clinical risk for LTBI and positivity on T-SPOT.TB or TST. CONCLUSION: T-SPOT.TB test was more frequently positive than TST in renal transplant candidates. However, further longitudinal studies are awaited to determine whether the ability of T-SPOT.TB assay to detect LTBI in renal transplant recipients can better predict the development of TB than can TST after transplantation.