Interferon-gamma Assays for the Diagnosis of Tuberculosis Infection Before Using Tumour Necrosis Factor-alpha Blockers

Objectives: Patients who receive tumour necrosis factor-alpha (TNF-alpha) blockers are mostly immunosuppressed. A study was performed to investigate whether an interferon-gamma (IFN-gamma) assay could represent an alternative approach to the tuberculin skin test (TST) for the diagnosis of latent tuberculosis infection (LTBI) in these patients.

Design: We prospectively enrolled 106 individuals into the study in two groups. Group 1 consisted of 38 healthy individuals and Group 2 included 68 patients with chronic inflammatory diseases evaluated for LTBI before the use of TNF-alpha blockers.

Results: Of all participants, nine had indeterminate IFN-gamma test results. Agreement between the two tests was poor in both groups (kappa values respectively -0.54 and 0.18). In a total of 97 subjects, 10 (10.3%) were positive by the IFN-gamma test and 49 (50.5%) by TST.

Conclusion: We found poor agreement between TST and the IFN-gamma test in our study. Our limited preliminary data should be accepted as a basis for designing future studies that will be helpful for physicians to decide whether the IFN-gamma test is more sensitive than the TST test in detecting LTBI before the use of TNF-alpha blockers.