UCSF

Objective

We sought to evaluate the test characteristics of Abbott ID-Now as a screening tool compared to polymerase chain reaction (PCR) testing for identification of COVID in an asymptomatic emergency department population.

Methods

We performed a prospective study enrolling a convenience sample of asymptomatic patients presenting to a single academic emergency department (ED) who received simultaneous testing with ID-Now and PCR per standardized ED protocols. Sensitivity, specificity, and positive and negative predictive value (PPV, NPV) of ID-Now were calculated compared to PCR. Stratified analysis by cycle threshold (Ct) values was also performed, defined as high viral load (Ct < 33) and low viral load (Ct ≥ 33).

Results

A total of 3121 patients were enrolled, of whom 2895 had valid results for ID-Now and PCR. COVID prevalence was 2.6%. ID-Now had a sensitivity of 85.1% (95% CI 75.9% to 92.7%) and a specificity of 99.7% (99.5% to 99.9%). PPV and NPV were high at 87.5% (83.1% to 96.1%) and 99.6% (99.3% to 99.8%). Stratified analysis by low and high Ct values demonstrated reduction in sensitivity in patients with low viral loads: 91.7% (81.6% to 97.2%) in low Ct value patients versus 58.3% (27.7% to 84.8%) in high Ct value patients.

Conclusions

ID-Now had excellent performance in asymptomatic ED patients with a low rate of false positives. Cycle threshold analysis suggests a relationship between viral load and ID-Now sensitivity. Given its speed and performance in this population, ID-Now should be considered an excellent tool to support clinical decision-making in ED populations.