To compare the Quantiferon-TB Gold test (QTF-G) with the tuberculin skin test (TST) for the detection of latent tuberculosis infection (LTBI) among patients with rheumatoid arthritis (RA) and ankylosing spondylitis (AS), with reevaluation of the patients treated with tumor necrosis factor-alpha (TNF-alpha) antagonists in the followup.
The study involved 140 consecutive patients, 82 with RA and 58 with AS. Thirty patients were evaluated with QTF-G for detection of LTBI before and after 6 months of TNF-alpha antagonist treatment. QTF-G was also performed on 49 healthy controls. QTF-G results were recorded as positive, negative, or indeterminate. A positive TST was defined as >or= 5 mm for RA and AS.
The percentages of positive QTF-G were comparable in RA and AS (37% vs 32%). The rate of positive QTF-G in healthy controls (29%) was also similar to RA and AS. In contrast to QTF-G results, a high rate of TST positivity was observed in AS compared to RA (82% vs 55%; p = 0.02). The total agreement between QTF-G and TST was observed to be 61% (kappa = 0.29) in the whole group, 70% (kappa = 0.42) in RA, and 49% (kappa = 0.14) in AS. After 6 months of treatment with TNF-alpha antagonists, a high rate of QTF-G change was observed in patients with indeterminate results (23% vs 3%; p = 0.03).
The comparable prevalence of LTBI among the study groups according to QTF-G supports the view that QTF-G is less susceptible to external factors than TST. Sequential testing for QTF-G in patients with indeterminate or negative results may also be helpful in discriminating LTBI better.