Introduction of a Borderline Range for the Interpretation of QuantiFERON-TB Gold In-Tube Results in Korean Healthcare Workers.

BACKGROUND

South Korea is the only Organisation for Economic Co-operation and Development (OECD) country with a high incidence of tuberculosis (TB). Healthcare workers (HCWs) have an increased risk of TB infection. QuantiFERON-TB Gold In-Tube (QFT-GIT) testing is performed for occupational health screening to detect latent TB infection (LTBI).

METHODS

We evaluated the introduction of new criteria for borderline ranges for interferon-gamma release assay (IGRA) results in HCWs. The results of QFT-GIT tests in HCWs in 2017 and 2018 were collected, with high-risk HCWs having two serial test results. Existing dichotomous criteria and new criteria with borderline ranges (bor-derline negative [BN], 0.20 - 0.34 IU/mL; borderline positive [BP], 0.35 - 0.99 IU/mL) were applied to each test re-sult.

RESULTS

After applying the borderline range, 26.4% of the positive results were classified as BP (4% of total results), while 4.2% of the negative results were classified as BN (3.6% of total results). Among seven HCWs with initial results in the borderline range, two had repeated borderline results while 71.4% had low negative results.

CONCLUSIONS

We recommend the introduction of borderline ranges in the interpretation of QFT-GIT results to reduce unnecessary TB therapy in HCWs.