Contribution of interferon-γ release assays (IGRAs) to the diagnosis of latent tuberculosis infection after renal transplantation.

BACKGROUND

Renal transplant recipients (RTRs), as all immunosuppressed patients, are at increased risk of reactivating latent tuberculosis infection (LTBI). Detecting LTBI in this population is therefore important to prevent active TB. The tuberculin skin test (TST) has a poor sensitivity in this setting.

METHODS

The aim of this prospective study was to compare the diagnostic performance of the TST and two interferon-γ release assays (IGRAs): T-SPOT.TB (Oxford Immunotec, Oxford, UK) and QuantiFERON Gold In-Tube (QGIT; Cellestis, Australia), performed simultaneously, for the detection of patients with risk factors for LTBI or a definite history of TB among RTRs under stable immunosuppression.

RESULTS

Two hundred five patients (ages 59±13 years, tested 10.4±7.1 years after transplantation) were studied. Positivity rate was 4.5% for TST, 20.5% for T-SPOT.TB, and 23.5% for QGIT. Agreement between IGRAs was fair (κ=0.71). Sensitivity of T-SPOT.TB and QGIT for detection of prior active TB was 55.6% (95% confidence interval [CI], 21.2-86.3) and 44.4 (95% CI, 13.7-78.8), respectively. Sensitivity of both IGRAs for detection of risk factors for LTBI was 33.3% (95% CI, 19.6-49.5). Specificity was 85.5% (95% CI, 78.9-90.7) for T-SPOT.TB and 80.1% (95% CI, 72.9-86.2) for QGIT. Combining IGRAs did not significantly improve sensitivity.

CONCLUSIONS

Because their sensitivity for detecting prior active TB and probable LTBI in RTRs is very low, IGRAs cannot be used to exclude LTBI. These results emphasize the limitations of IGRAs in the setting of chronic immunosuppressive therapy.