To compare the performance of QuantiFERON-TB Gold (QFT-G) with that of the tuberculin skin test (TST) in detecting latent tuberculosis (LTBI) among patients with rheumatoid arthritis (RA).
A total of 35 RA patients and 15 healthy controls underwent TST, QFT-G assays and chest X-ray and filled out a questionnaire on predisposing conditions for TB disease. Serum interferon gamma (IFN-gamma) levels were tested by an enzyme-linked immunosorbent assay.
Forty-five per cent of RA patients had a TST > 5 mm vs. 26% in healthy controls. In the RA patients, QFT-G was positive in 11.4%, negative in 60% and indeterminate in 28.6%. The overall agreement between TST and QFT-G was significantly lower in the RA population than in controls (56% vs. 84%). No correlation was found between the use of prednisone, methotrexate and QFT-G results or agreement between TST and QFT-G. A low IFN-gamma level (<4 pg/ml) was found in 51.5% of the RA patients. No correlation was found between serum IFN-gamma levels and QFT-G results.
The clinical significance of negative QFT-G in TST-positive patients with low TB risk remains to be assessed. The high rate of indeterminate results questions the clinical utility of QFT-G in the diagnosis of LTBI in RA patients.