COVID-19 Evidence Alerts
from McMaster PLUSTM

Current best evidence for clinical care (more info)

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Diagnosis Mockel M, Corman VM, Stegemann MS, et al. SARS-CoV-2 antigen rapid immunoassay for diagnosis of COVID-19 in the emergency department. Biomarkers. 2021 May;26(3):213-220. doi: 10.1080/1354750X.2021.1876769. Epub 2021 Feb 18.

BACKGROUND: In the emergency department (ED) setting, rapid testing for SARS-CoV-2 is likely associated with advantages to patients and healthcare workers, for example, enabling early but rationale use of limited isolation resources. Most recently, several SARS-CoV-2 rapid point-of-care antigen tests (AGTEST) became available. There is a growing need for data regarding their clinical utility and performance in the diagnosis of SARS-CoV-2 infection in the real life setting EDs.

METHODS: We implemented AGTEST (here: Roche/SD Biosensor) in all four adult and the one paediatric EDs at Charité - Universitätsmedizin Berlin in our diagnostic testing strategy. Test indication was limited to symptomatic suspected COVID-19 patients. Detailed written instructions on who to test were distributed and testing personnel were trained in proper specimen collection and handling. In each suspected COVID-19 patient, two sequential deep oro-nasopharyngeal swabs were obtained for viral tests. The first swab was collected for nucleic acid testing through SARS-CoV-2 real-time reverse transcriptase (rt)-PCR diagnostic panel (PCRTEST) in the central laboratory. The second swab was collected to perform the AGTEST. Analysis of routine data was prospectively planned and data were retrieved from the medical records after the inclusion period in the adult or paediatric ED. Diagnostic performance was calculated using the PCRTEST as reference standard. False negative and false positive AGTEST results were analysed individually and compared with viral concentrations derived from the calibrated PCRTEST.

RESULTS: We included n = 483 patients including n = 202 from the paediatric ED. N = 10 patients had to be excluded due to missing data and finally n = 473 patients were analysed. In the adult cohort, the sensitivity of the AGTEST was 75.3 (95%CI: 65.8/83.4)% and the specificity was 100 (95%CI: 98.4/100)% with a SARS-CoV-2 prevalence of 32.8%; the positive predictive value was 100 (95%CI: 95.7/100)% and the negative predictive value 89.2 (95%CI: 84.5/93.9)%. In the paediatric cohort, the sensitivity was 72.0 (95%CI: 53.3/86.7)%, the specificity was 99.4 (95%CI:97.3/99.9)% with a prevalence of 12.4%; the positive predictive value was 94.7 (95%CI: 78.3/99.7)% and the negative predictive value was 96.2 (95%CI:92.7/98.3)%. Thus, n = 22 adult and n = 7 paediatric patients showed false negative AGTEST results and only one false positive AGTEST occurred, in the paediatric cohort. Calculated viral concentrations from the rt-PCR lay between 3.16 and 9.51 log10 RNA copies/mL buffer. All false negative patients in the adult ED cohort, who had confirmed symptom onset at least seven days earlier had less than 5 × 105 RNA copies/mL buffer.

CONCLUSIONS: We conclude that the use of AGTEST among symptomatic patients in the emergency setting is useful for the early identification of COVID-19, but patients who test negative require confirmation by PCRTEST and must stay isolated until this result becomes available. Adult patients with a false negative AGTEST and symptom onset at least one week earlier have typically a low SARS-CoV-2 RNA concentration and are likely no longer infectious.

Discipline / Specialty Area Score
Emergency Medicine
Hospital Doctor/Hospitalists
Internal Medicine
Pediatric Emergency Medicine
Infectious Disease
Comments from MORE raters

Emergency Medicine rater

Interesting study. There is a burgeoning rapid-test literature but little of it focuses on the ED setting. These findings confirm the general literature on limited sensitivity but good specificity. The questions are: Does the test improve on clinical judgement and validated rules? If patients still need to isolate, what added benefit does the rapid test really bring?

Emergency Medicine rater

Readily available point-of-care COVID-19 testing for ED patients are still required >1 year into this global pandemic. This research provides accuracy data for one rapid antigen test and appropriately suggests caution when applying this test to adults.

Emergency Medicine rater

This is useful information in rapidly evolving changes in this field.

Hospital Doctor/Hospitalists rater

It is very useful to have effectiveness data for antigen assays, and the takeaway about the TP vs FN is potentially very useful for patient flow. One concern I have is that I do not believe it is necessarily practical to do both tests at the same time (as the authors suggest), especially in resource-poor environments or in areas experiencing a surge. Regardless, the data presented can be used by different hospital ID/infection control committees.

Pediatric Emergency Medicine rater

With the COVID-19 pandemic, early and rapid identification is critical for treatment and further spread of the disease. Several rapid tests were made available for use in the emergency departments, however, a number of false-negative tests were observed. This may be associated with a broad variation in virus concentration, so negative AGTEST results should be interpreted with caution. A confirmation is needed for patients who test negative. This study underscores the need to develop rapid and reliable tests to prevent further transmission.