Dynamic changes in positive interferon-gamma release assay in a dialysis population: An observational cohort study

Background: Interferon-gamma release assay (IGRA) is popular for detecting latent tuberculosis infection (LTBI), but its dynamic change is uncertain in high-risk groups such as dialysis patients.

Methods: Patients undergoing dialysis were prospectively enrolled. The QuantiFERON-TB Gold In-Tube (QFT-GIT) was used to detect LTBI. After 6 and 12 months, QFT-GIT was repeated to monitor dynamic changes.

Results: Only 204 of 391 enrolled patients completed the study. The initial QFT-GIT positive rate of 22.1% decreased to 19.6% after 6 months and to 14.2% after 12 months. The 6-month reversion rate was 45.9% while the conversion rate was 7.7%. Sub-population with new QFT-GIT positivity had 87.5% reversion rate, higher than the 20.8% of patients with persistent QFT-GIT positivity. The QFT-GIT response was independently associated with persistent QFT-GIT positivity. Using 0.93 IU/ml of the initial QFT-GIT response as the threshold can detect 79% persistent positivity in 6-month follow-up. Prior TB had a borderline significance for predicting conversion.

Conclusions: In the dialysis population, reversion and conversion occur frequently within six months. The QFT-GIT positive population is heterogeneous and sub-populations have different reversion rates. Higher QFT-GIT positivity threshold can identify patients with persistent QFT-GIT positivity to prioritize follow-up and LTBI therapy.