The following is a summary of “Diagnostic performance of rapid antigen tests for SARS-CoV-2 transmission risk based on cycle threshold values in the emergency department,” published in the December 2023 issue of Emergency Medicine by Lee, et al.

For a study, researchers sought to assess the diagnostic efficacy of rapid antigen tests (RATs) in screening patients with specific cycle threshold (Ct) values of SARS-CoV-2 reverse transcription-polymerase chain reaction (RT-PCR) in the emergency department. Ct values have been previously recognized as potential indicators of infectiousness, hence their consideration in this study.

A retrospective observational study was conducted at a single center between January 1, 2020, and March 31, 2022. The study included patients who underwent RT-PCR and RAT for COVID-19 diagnosis, excluding those with negative RT-PCR results. Patients with Ct values below 26 and 30 were identified as potentially infectious for COVID-19.

A total of 386 patients were analyzed. At Ct value cutoffs of 26 and 30, the RAT demonstrated a sensitivity of 82% and 74%, specificity of 84% and 89%, and area under the curve (AUC) of 0.829 and 0.813, respectively, in the receiver operating characteristic curve. However, the negative predictive value (NPV) was relatively low at 55% and 25%.

The RAT may be a rapid screening tool for identifying patients with potentially infectious SARS-CoV-2. Nonetheless, due to the low NPV, relying solely on negative RAT results to end quarantine may be challenging. Clinicians are advised to consider additional factors such as symptom duration and immunocompromised status when evaluating SARS-CoV-2 transmission risk.

Reference: sciencedirect.com/science/article/abs/pii/S0735675723004898