Delineating a Retesting Zone Using Receiver Operating Characteristic Analysis on Serial QuantiFERON Tuberculosis Test Results in US Healthcare Workers

Abstract EN

Objective.

To find a statistically significant separation point for the QuantiFERON Gold In-Tube (QFT) interferon gamma release assay that could define an optimal “retesting zone” for use in serially tested low-risk populations who have test “reversions” from initially positive to subsequently negative results.

Method.

Using receiver operating characteristic analysis (ROC) to analyze retrospective data collected from 3 major hospitals, we searched for predictors of reversion until statistically significant separation points were revealed.

A confirmatory regression analysis was performed on an additional sample.

Results.

In 575 initially positive US healthcare workers (HCWs), 300 (52.2%) had reversions, while 275 (47.8%) had two sequential positive tests.

The most statistically significant (Kappa = 0.48, chi-square = 131.0, P<0.001) separation point identified by the ROC for predicting reversion was the tuberculosis antigen minus-nil (TBag-nil) value at 1.11 International Units per milliliter (IU/mL).

The second separation point was found at TBag-nil at 0.72 IU/mL (Kappa = 0.16, chi-square = 8.2, P<0.01).

The model was validated by the regression analysis of 287 HCWs.

Conclusion.

Reversion likelihood increases as the TBag-nil approaches the manufacturer's cut-point of 0.35 IU/mL.

The most statistically significant separation point between those who test repeatedly positive and those who revert is 1.11 IU/mL.

Clinicians should retest low-risk individuals with initial QFT results < 1.11 IU/mL.