Fig. 2.

Performance of complete blood count (CBC)-based predictive COVID-19 rule-out tool. A) Results of predictive tool on Stanford Health Care emergency department patient cohort. B) Results of predictive tool on a Seattle, Washington emergency department patient cohort. C) Results of predictive tool on a Chicago, Illinois emergency department patient cohort. D) South Korean cohort of emergency department patients. All four cohorts represented validation sets not previously seen by the decision support tool. SARS-CoV-2 PCR performed in local laboratories was used as the reference method. Left: Receiver operating characteristic curves. Middle: Specificity versus negative predictive value across all operating thresholds. Right: Confusion matrix calculated using operating point defined using Stanford Health Care training cohort. AUC: Receiver operating characteristic area under curve. PPV: positive predictive value. NPV: negative predictive value. Avg. NPV: Weighted average of negative predictive values with specificity as weights across all probability thresholds. Always neg. model: baseline negative predictive value expected by a classifier that always predicts SARS-CoV-2 negative.