Background: Tumour necrosis factor-alpha (TNF-α) inhibitors have been introduced in the treatment of refractory sarcoidosis. These biologics may reactivate latent tuberculosis infection (LTBI). Despite its known limitations, the tuberculin skin test (TST) is currently used for the diagnosis of LTBI in Danish sarcoidosis patients. We report the results of a screening using the interferon-gamma release assay (IGRA) QuantiFERON TB Gold (QFN) for the diagnosis of LTBI. We aimed to assess whether the QFN is reliable for diagnosing LTBI among sarcoidosis patients and if results are influenced by disease activity or immunosuppressive treatment.
Methods: A prospective study was performed from 2005 to 2007 among sarcoidosis patients who were candidates for TNF-α inhibitor treatment. Information on immunosuppressive treatment was obtained from the medical records. Disease activity was assessed by biochemistry, chest roentgenograms and pulmonary function tests. The predictive value of QFN results was evaluated by follow-up in the Danish National Tuberculosis Registry.
Results: A total of 44 sarcoidosis patients (22 men) with a median age of 39 y (range 25-59 y) were enrolled; 93% had a negative QFN test result and 7% had an indeterminate result. Forty-three percent had disease activity and 57% (n = 25) received immunosuppressive treatment. There was no significant difference in QFN interferon-γ response between subjects with or without disease activity (p > 0.4) and between treated vs non-treated patients (p > 0.5). At follow-up using the Danish tuberculosis registry, there was no occurrence of tuberculosis among study participants.
Conclusions: The predictive value of the QFN seems good among Danish sarcoidosis patients and the results appear to be unaffected by sarcoidosis disease activity and immunosuppressive treatment.