Interferon-gamma release assays versus tuberculin skin testing for detection of latent tuberculosis in chronic haemodialysis patients.

BACKGROUND End stage renal disease increases the risk of reactivating latent tuberculosis (LTBI). Interferon-gamma release assays (IGRA) are an alternative to the tuberculin skin test (TST) for detecting LTBI. METHODS Sixty-two hemodialysis patients (46 male, 16 female, aged 65 +/- 15 years) from 3 hemodialysis facilities in the Geneva area were submitted to a TST, 2 IGRA (T-SPOT.TB and QuantiFERON Gold in tube: QFT), a chest radiography, and a questionnaire to record social status, country of birth, history of prior TST, tuberculosis (TB), BCG (Bacillus of Calmette-Guérin vaccine), and any cause of immuno-suppression. LTBI was defined as prior "at risk" contact with a case of contagious TB and/or a chest X-ray suggestive of prior TB infection. RESULTS Positivity rate was 19% for TST, 21% for QFT and 29% for T-SPOT-TB; 8% of QFT and 11% of T-SPOT-TB were indeterminate. Agreement between IGRA was fair (kappa = 0.60). After adjusting for age and BCG, OR (Odds Ratio) of having a positive QFT was 4.6-fold (p = 0.029) higher in patients with LTBI vs. those without LTBI. In contrast, no association was found between LTBI and having a positive T-SPOT.TB or a positive TST. As expected, there was a strong association between prior BCG vaccination and having a positive TST (OR 5.3, p = 0.017). QFT was the only test with a significant OR of having LTBI (adjusted OR: 4.4; 95%CI: 1.1 - 17.6; p = 0.034). Among 5 patients with definite prior TB, TST and T-SPOT.TB were positive in 1 and QFT, in 2. CONCLUSIONS In this population, QFT was superior to TST for detecting LTBI, but both IGRAs and TST have important limitations, and are unreliable for screening for LTBI.