New CDC study finds that Abbott BinaxNOW SARS-CoV-2 antigen test is substantially less sensitive than PCR testing
When the first COVID-19 antigen test became available for public use in early May of 2020, the test was viewed as having great potential for enabling widespread SARS-CoV-2 testing. The game changer of such rapid antigen tests was that they could run a turnaround time of less than 30 minutes and be performed at the point of care (POC). Polymerase chain reaction (PCR) testing, in comparison, required specimens to be sent to a clinical laboratory, subject to longer turnaround time to result (up to seven days).
While antigen testing seemed to fill a need that PCR testing could not, it was quickly recognized that these tests showed a substantial downside. The sensitivity of the rapid antigen tests appeared to be much lower than the sensitivity of PCR testing. The lesson learned was that false positives began to unnecessarily disrupt the entities and individuals relying on them. This downside has long been recognized, even as millions of tests were distributed and used across the country. However, still debated is the extent to which the issue affects the utility of these tests.
Now we know that the US Centers for Disease Control and Prevention (CDC) appears to be keeping a watchful eye, showing recent interest in understanding the public utility of rapid antigen testing and how useful these tests are when compared to PCR testing. A study posted Jan. 19, 2021, in the CDC’s Morbidity and Mortality Weekly Report (MMWR) provides clinical laboratories and other clinicians with more information on this subject.
Performance of Abbott BinaxNOW SARS-CoV-2 Antigen Test
Researchers examined the sensitivity and specificity of one antigen test specifically—the Abbott BinaxNOW SARS-CoV-2 antigen test. They compared this test’s performance to PCR testing, analyzing 3,419 specimens.
“In this evaluation, using real-time RT-PCR as the standard, the sensitivity of the BinaxNOW antigen test was lower among specimens from asymptomatic persons (35.8%) than among specimens from symptomatic persons (64.2%),” the study’s authors wrote regarding their findings. “Specificity (99.8%–100%) was high in specimens from both asymptomatic and symptomatic groups.”
The low sensitivity, especially for asymptomatic individuals, reinforces previous research that shows a higher number of false positives when using antigen testing. This does not necessarily mean, however, that antigen testing is not useful, according to Jessica Prince-Guerra, PhD, of CDC’s Laboratory and Testing Task Force and one of the study’s authors.
“Despite a lower ability to detect infection, the quick turnaround time of the BinaxNOW antigen test can help in rapidly identifying people with COVID-19 so they can be isolated, particularly when used as part of repeated testing strategies,” Prince-Guerra said in a statement. “However, everyone, regardless of test results, should wear a mask, avoid gatherings, and stay at least six feet from others.”
More Key Findings of Abbott BinaxNow COVID-19 Study
One of the key findings in this study published in the MMWR is that specificity is still quite high with antigen testing. This allows those who use antigen testing to be as confident in a negative infection status as would be expected with COVID-19 PCR testing.
Researchers also suggested that the rapid turnaround time has advantages when initiating contact tracing measures. “Persons who know their positive test result within 15–30 minutes can isolate sooner and contact tracing can be initiated sooner and be more effective than if a test result is returned days later,” the researchers wrote. “Serial antigen testing can improve detection, but consideration should be given to the logistical and personnel resources needed.”
Clinical laboratory leaders should consider the information that the CDC has provided about the utility of antigen testing, even though it has been shown to result in more false positives than PCR testing. Perhaps even as important as the information itself is the fact that this information comes from the CDC and may indicate that the CDC is likely to consider antigen testing as useful, and even essential, despite its potential downsides.
—By Caleb Williams, Editor, COVID-19 STAT
