Current best evidence for clinical care (more info)
The use of Antigen point of care tests (AgPOCT) might be an essential tool to fight the coronavirus disease 2019 (COVID-19) pandemic. Manufacturer information indicates a specificity of about 95% and there is a growing interest to use these tests area-wide. Therefore, it is necessary to clarify whether AgPOCT can be used safely for "rule-in" (detection of positive patients) and for "rule-out" (valid negative testing). Two thousand three hundred and seventy-five patients received polymerase chain reaction (PCR) testing and AgPOCT for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) regardless of symptoms. The positive predictive value of symptomatic and asymptomatic patients was compared with a cut-off threshold cycle (Ct ) value of =30 and in total. Five hundrded and fifty-one patients tested positive for the SARS-CoV-2 virus by PCR, of whom 35.2% presented without symptoms. In all patients, regardless of their symptoms or Ct values, a sensitivity of 68.9% and a specificity of 99.6% were calculated for AgPOCT. In patients with Ct values =30, a sensitivity of 80.5% (95% confidence interval: ±1.62) and a specificity of 99.6% were shown for all tests (symptomatic/asymptomatic). Highly infectious patients (Ct = 20), regardless of symptoms, were reliably detected by the AgPOCT. In infectious patients with Ct values =30, the test has a sensitivity of about 80% regardless of COVID-19 typical symptoms, which is apparently less than the 96.52% specificity indicated by the manufacturer. Relevant improvement in test sensitivity by querying the patients who are symptomatic and asymptomatic is also not feasible. We strongly suggest that we critically question the use of AgPOCT for "rule-out," as they only provide a supposed safety.
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Although the manufacturer apparently states the sensitivity of their Ag test is higher, this is consistent with all the other data. I've seen suggesting Ag testing is not very sensitive. It is also being compared against a gold standard PCR test that is generally about 70% sensitive. At least in the US, rapid PCR tests are fairly available now, making this less an issue.
A 20-30% miss is too high.
It is important to have a clear understanding of the Bayesian approach to this issue. As the article points out, the test is currently of questionable value in ruling out due to its low sensitivity. Those individuals who are encouraging people not to get vaccinated are presenting claims that it is a useless test, so we need to keep on top of this information. There is great positive predictive value, and great at identifying infectious cases. However, it's of questionable use in ruling it out.
As an infectious diseases consultant, I found this review of data on the sensitivity and specificity of SARS-CoV2 rapid antigen testing useful in confirming the lack of sensitivity of these tests.
It's important to know that the real life COVID antigen point of care tests (AgPOCT) is only 80.5% sensitive.
This article checks the performance of Covid-19 rapid antigen test in a well developed study in real life. It gets the results that we already know; the yields in real life use are lower than the "experimental" results indicated by a the manufacturer.