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.