Inter-rater reliability and prospective validation of a clinical prediction rule for SARS-CoV-2 infection

Accurate estimation of the risk of SARS-CoV-2 infection based on bedside data alone has importance to emergency department (ED) operations and throughput. The 13-item CORC (COVID [or coronavirus] Rule-out Criteria) rule had good overall diagnostic accuracy in retrospective derivation and validation. The objective of this study was to prospectively test the inter-rater reliability and diagnostic accuracy of the CORC score and rule (score ≤ 0 negative, > 0 positive) and compare the CORC rule performance with physician gestalt.

This noninterventional study was conducted at an urban academic ED from February 2021 to March 2021. Two practitioners were approached by research coordinators and asked to independently complete a form capturing the CORC criteria for their shared patient and their gestalt binary prediction of the SARS-CoV-2 test result and confidence (0%-100%). The criterion standard for SARS-CoV-2 was from reverse transcriptase polymerase chain reaction performed on a nasopharyngeal swab. The primary analysis was from weighted Cohen's kappa and likelihood ratios (LRs).

For 928 patients, agreement between observers was good for the total CORC score, κ = 0.613 (95% confidence interval [CI] = 0.579-0.646), and for the CORC rule, κ = 0.644 (95% CI = 0.591-0.697). The agreement for clinician gestalt binary determination of SARs-CoV-2 status was κ = 0.534 (95% CI = 0.437-0.632) with median confidence of 76% (first-third quartile = 66-88.5). For 425 patients who had the criterion standard, a negative CORC rule (both observers scored CORC < 0), the sensitivity was 88%, and specificity was 51%, with a negative LR (LR-) of 0.24 (95% CI = 0.10-0.50). Among patients with a mean CORC score of >4, the prevalence of a positive SARS-CoV-2 test was 58% (95% CI = 28%-85%) and positive LR was 13.1 (95% CI = 4.5-37.2). Clinician gestalt demonstrated a sensitivity of 51% and specificity of 86% with a LR- of 0.57 (95% CI = 0.39-0.74).

In this prospective study, the CORC score and rule demonstrated good inter-rater reliability and reproducible diagnostic accuracy for estimating the pretest probability of SARs-CoV-2 infection.