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.