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

Figure 1

Receiver operating characteristic (ROC) decision tree identifying statistically significant TBag-nil (in IU/mL) separation points which predict those HCWs with a positive TB test result at time one who retest negative at time two. Logistic regression analysis on a separate Confirmatory sample of 287 HCWs validated all 3 separation points at 0.72, 1.11, and 2.17 IU/mL and remained statistically significant for all subgroups by chi-square (𝑃<0.001). 1 Kappa=0.48, chi-square=131.0, 𝑃<0.001, 2 Kappa=0.16, chi-square=8.2, 𝑃<0.01, 3 Kappa=0.27, chi-square=20.4, 𝑃<0.001.