Comparative evaluation of four SARS-CoV-2 antigen tests in hospitalized patients

Abstract

Objectives Rapid identification of infected subjects is a corner stone for control of a pandemic like the current one with the SARS-CoV-2. Easy to handle antigen tests can provide timely results which is of specific importance in a primary care setting. However, concerns exist regarding their sensitivity, which let us evaluate four commercially available tests in patients hospitalized for COVID-19. Methods We analyzed in parallel nasopharyngeal/oropharyngeal swabs from 87 consecutive patients admitted to our department with moderate to severe COVID-19 by means of quantitative RT-PCR (Cobas, Roche) and up to four antigen tests from different distributors. Antigen test results were linked to Ct (cycle threshold) values as a marker for infectivity of patients. Results We found that two out of four antigen tests correctly identified subjects with high viral loads (Ct ≤25) and three out of four tests detected more than 80% of subjects with a Ct ≤30 which is considered as a threshold for infectivity. However, one test investigated had a poor clinical performance. When investigating subjects with Ct values >30 we found that in up to 45% of the cases the antigen test was still positive. Conclusion Most antigen tests had a sufficient sensitivity to identify symptomatic subjects infected with SARS-CoV-2 and with transmissible infection. On the other hand, antigen testing may not be suitable to identify loss of infectivity in COVID-19 subjects during follow-up. Newly introduced antigen tests need to be validated in a clinical or primary care setting to define their clinical usefulness.

Comparison of SARS-CoV-2 Detection by Rapid Antigen and by Three Commercial RT-qPCR Tests: A Study from Martin University Hospital in Slovakia

“…However, after the analyses of Ct values, it can be seen that subjects that were both antigen and RT-qPCR positive had mean and median Ct values for Sarbeco E and RdRP genes amounting to about 20, whereas the antigen-negative but RT-qPCR-positive samples had these measures of centre close to 30 (details are in Table 2). The inability to detect samples with higher Ct values is in line with the results of Thommes et al When investigating subjects with Ct values higher than 30, the antigen tests were positive in no more than 45% of such cases [17]. If the cycle threshold (Ct) values are taken as viral load indicators and prediction markers [32][33][34], it may be considered a strength of this antigen test (Standard Q COVID-19 Ag test, SD Biosensor) that it detects people at higher risk both on the personal level (risk of more severe disease) and on the population level (risk of viral shedding and transmission).…”

“…Under regulations issued by the Ministry of Health of the Slovak Republic, hospital employees are obliged to undergo testing using state-supplied antigen tests every second week. However, many questions were raised about the suitability of the selected testing method, especially regarding its use with large numbers of healthcare professionals and its effectiveness where individuals have low viral load [ 17 , 18 , 19 ].…”

Performance evaluation of automated chemiluminescence immunoassay based antigen detection – Moving towards more reliable ways to predict SARS-CoV-2 infection

“…In our study we have considered Ct value of 35 on RT-PCR as positive. However, with Ct values of 25 which corresponds to high viral load, conventional card based antigen detection tests (RAT) shows better sensitivity ( Thommes et al, 2021 ; Pickering et al, 2021 ). Therefore, we also evaluated the performance of VITROS, and RAT based on Ct value of 25.…”

Applications of laboratory findings in the prevention, diagnosis, treatment, and monitoring of COVID-19

“…However, one investigated test had a poor clinical performance. 155 Bruzzone et al have quantified the performance of seven different available types of antigendetecting rapid diagnostic tests compared with RT-qPCR, and the results showed that the overall sensitivity and specificity of antigen tests were 78.7% and 100%, respectively, and a wide range of sensitivity of different brands (66.0-93.8%) was observed. 156 Therefore, further investigations and confirmatory studies are needed for the validation of different antigendetection kits.…”