Diagnostic accuracy of the Abbott ID NOW SARS-CoV-2 rapid test for the triage of acute medical admissions

Abstract

Background: Decisions to isolate patients at risk of having coronavirus disease 2019 (COVID-19) in the emergency department (ED) must be rapid and accurate to ensure prompt treatment and maintain patient flow whilst minimising nosocomial spread. Reverse transcription polymerase chain reaction (RT-PCR) assays are too slow to achieve this, and near-patient testing is being used increasingly to facilitate triage. The ID NOW severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) assay is an isothermal nucleic acid amplification near-patient test which targets the RNA-dependent RNA-polymerase gene.

Aim: To assess the diagnostic performance of ID NOW as a COVID-19 triage tool for medical admissions from the ED of a large acute hospital.

Methods: All adult acute medical admissions from the ED between 31^st March and 31^st July 2021 with valid ID NOW and RT-PCR results were included. The diagnostic accuracy of ID NOW [sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV)] was calculated against the laboratory reference standard. Discrepant results were explored further using cycle threshold values and clinical data.

Findings: Two percent (124/6050) of medical admissions were SARS-CoV-2 positive on RT-PCR. Compared with PCR, ID NOW had sensitivity and specificity of 83.1% [95% confidence interval (CI) 75.4-88.7] and 99.5% (95% CI 99.3-99.6), respectively. PPV and NPV were 76.9% (95% CI 69.0-83.2) and 99.6% (95% CI 99.5-99.8), respectively. The median time from arrival in the ED to ID NOW result was 59 min.

Conclusion: ID NOW provides a rapid and reliable adjunct for the safe triage of patients with COVID-19, and can work effectively when integrated into an ED triage algorithm.

Keywords: COVID-19; Emergency department; ID NOW; Near-patient testing; SARS-CoV-2; Triage.

Figure 1

Study flow-chart. RT-PCR, real-time polymerase chain reaction; ED, emergency department; COVID-19, coronavirus disease 2019; CDU, clinical decision unit; ICU, intensive care unit.

Figure 2

Time from arrival at the emergency department (ED) to ID NOW result. Time between arrival at the ED and a valid ID NOW result becoming available was calculated for each admission. These data are presented as a histogram (A) showing the distribution of time to ID NOW result for all admissions (N=6050). Kaplan–Meier time-to-event curves showing the proportion of admissions with a valid ID NOW result within the first 4 h after arrival at the ED are shown (B). 95% confidence intervals are shown. Admissions requiring supplemental oxygen on arrival (red) are compared with admissions not requiring supplemental oxygen on arrival (blue) (B) (N=5816, 3.9% missing data).