Fig. 4

Fagan`s nomogram showing probability of COVID-19 infection after chest CT diagnosis. a Probabilities were calculated based on the reference standard of RT-PCR test only or b RT-PCR and/or AB test. Positive CT diagnosis (blue arrow) refers to typical or nonspecific appearance, and negative CT diagnosis (red arrow) to atypical or negative appearance of CT scan. Precision is given as 95% confidence interval. Disease prevalence is derived from the number of COVID-19 positive and negative participants. AB, antibody test; CT, low-dose chest computed tomography; LR+, positive likelihood ratio; LR−, negative likelihood ratio; NPV, negative predictive value; PPV, positive predictive value; RT-PCR, reverse transcription polymerase chain reaction