key: cord-0684472-6oahs1y3
authors: Bräunlich, Jens; Hoheisel, Reimund; Dinse-Lambracht, Alexander
title: Comparison of SARS-CoV-2 antigen testing to RT-PCR in a real-world setting – an observational cohort study
date: 2021-09-23
journal: Diagn Microbiol Infect Dis
DOI: 10.1016/j.diagmicrobio.2021.115531
sha: 5a8864074e88de6894faa5e5421b98c2297ad8ba
doc_id: 684472
cord_uid: 6oahs1y3

A total of 2978 patients with validated paired results (SARS-CoV2-antigen and PCR) were identified. Our results show that only 45 antigen tests from 90 patients with positive validated PCR were correctly identified by antigen testing (sensitivity 50%). Roughly 50% of these patients had ongoing respiratory symptoms.

Jens Bräunlich MD PD 1,* highflow@web.de, Reimund Hoheisel MD 2 

The ongoing CoV2 pandemic with its economic and educational considerations led to an understandable debate about the end of restrictions with the now ubiquitous availability of vaccinations. In addition to the PCR as the state-of-the art detection method, antigen testing has become a very popular tool in the effort to relieve restrictions and reopen society. In anticipation of widespread antigen testing, it has been perceived by the public as a diagnostic tool with a high standard of safety and diagnostic accuracy.

We retrospectively analyzed a large cohort of subjects in a low incidence area. Through this approach a total of 2978 patients with validated paired results (antigen and PCR) were identified. Our results show that only 45 antigen tests from 90 patients with positive validated PCR were correctly identified by antigen testing. Roughly 50% of these patients had ongoing respiratory symptoms.

To our knowledge this is the biggest observational study to date investigating the safety of antigen testing compared to PCR in a real-world environment. The results of our study can help to calculate the risk of an antigen-based testing strategy as basic for "opening strategy" in the ongoing pandemic.

Abstract: A total of 2978 patients with validated paired results (SARS-CoV2-antigen and PCR) were identified. Our results show that only 45 antigen tests from 90 patients with positive validated PCR were correctly identified by antigen testing (sensitivity 50%). Roughly 50% of these patients had ongoing respiratory symptoms.

The ongoing CoV2 pandemic with its economic and educational considerations led to an understandable debate about the end of restrictions with the now ubiquitous availability of vaccinations. In addition to the RT-PCR as the state-of-the art detection method, antigen testing has become a very popular tool in the effort to relieve restrictions and reopen society. In anticipation of widespread antigen testing, it has been perceived by the public as a diagnostic tool with a high standard of safety and diagnostic accuracy. The proportion of false negatives is a well-established problem that must be kept in mind when considering the easing of restrictions on the population during this pandemic 1,2 . There are many factors which determine the accuracy of antigen testing 3, 4 . To describe the situation of broad antigen testing as part of an "end-of-restriction" strategy we analyzed a large cohort of subjects in a low incidence area retrospectively, to illustrate such a real-world testing scenario. Table 1 shows the results of the antigen/RT-PCR pairs of our study group.

The positive predictive value was 0,68, negative predictive value was 0,99. The sensitivity/ true positive rate was 0,5. Our results show that only 45 antigen tests from 90 patients with positive validated PCR were correctly identified by antigen testing. Roughly 50% of these patients had ongoing respiratory symptoms. Asymptomatic carriers of SARS-CoV-19 as well as subjects with transmission potential could have led to a higher false negative rate.

To our knowledge this is the biggest observational study to date investigating the safety of antigen testing compared to PCR in a real-world environment. We found true positive In mixed populations with a high percentage of asymptomatic people the sensitivity of antigen tests is poorly described. The (mass) antigen test allows to screen at-risk populations and could allow faster return to working places or other institutions. The situation of a low incidence and a high percentage of asymptomatic people illustrates best the current worldwide situation and our study setting. In addition, our testing strategy described above may be of value as a mass screening in a population at higher risk for infection. Our study reflects the current situation in 3 hospitals and provide evidence of future testing strategies for these institutions. The results are in line with studies in asymptomatic cohorts 4 . Our results provide evidence of usefulness and limitations of antigen tests and leads to several implications.

Symptomatic people with negative antigen tests should be handled with caution and should in addition undergo RT-PCR testing. In the ongoing pandemic antigen testing should be combined with established protection policies to maximise "anti-pandemic" effects. The low sensitivity of antigen tests in asymptomatic persons as demonstrated by our study and the growing general availability of antigen testing may give rise to an unwarranted carelessness.

The results of our study may help to calculate the risk of an antigen-based testing strategy more accurately and provide a base for an "opening strategy" in the ongoing pandemic. 

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Rapid, point-of-care antigen and molecular-based tests for diagnosis of SARS-CoV-2 infection

Validation testing to determine the effectiveness of lateral flow testing for asymptomatic SARS-CoV-2 detection in low prevalence settings

All authors contributed to the design and implementation of the research, to the analysis of the results and to writing of the manuscript.All authors declare no conflict of interest.JB is the guarantor of the paper, taking responsibility for the integrity of the work as a whole, from inception to published article mmc1.docx mmc2.docx mmc3.docx