Accuracy of Rapid COVID Test Subpar in Children Aged 7 and Older, Researchers Say

By Megan Brooks

September 01, 2021

NEW YORK (Reuters Health) - The BinaxNOW rapid SARS-CoV-2 antigen detection assay from Abbott does "not seem particularly useful" in symptomatic children and young adults aged 7 to 20 years due to "suboptimal" sensitivity and specificity, researchers say.

In symptomatic children younger than age 7, the test's specificity is also "suboptimal" but its high sensitivity might be useful in ruling out COVID-19, report Dr. Nader Shaikh and colleagues of the University of Pittsburg Medical Center and Children's Hospital of Pittsburgh in Pediatrics.

If these findings are confirmed by others, children younger than age 7, with a negative BinaxNOW result "could be allowed to return to day care or preschool. However, positive results would need to be confirmed with a PCR test, given the test's high false-positive rate," they suggest.

But Dr. Michael Mina, an expert in diagnostic testing who wasn't involved in the study, cautioned that "it's "an extremely small sample size" and the results are "an outlier and when you have an outlier with such a small sample, it really raises questions."

"There are studies now with 10s of 1000s of these tests being run that really shows specificity of like, 99.9%," Dr. Mina, with Harvard's T.H. Chan School of Public Health, Boston, told Reuters Health by phone.

For their study, the Pittsburgh researchers tested 199 children aged two months to 20 years with symptoms suggestive of COVID-19 for less than one week. They all had one of the following symptoms: cough, shortness of breath, difficulty breathing, loss of smell or taste, severe respiratory illness; or two of the following: known exposure to COVID-19, fever or chills, congestion or runny nose, body aches, fatigue, headache, sore throat, nausea, vomiting, or diarrhea.

They calculated the accuracy of the BinaxNOW assay using PCR results as the reference standard.

Of the 199 children, 39 had a positive PCR for SARS-CoV-2. In the overall cohort, the sensitivity and specificity of BinaxNOW were 85% and 91%, respectively.

The accuracy of the test was higher in children younger than age 7 years (sensitivity, 100%; specificity, 92%). In children aged 7 to 20 years, sensitivity was 79% and specificity 90%.

"The conclusion of the study is that the test is not as accurate as widely assumed," Dr. Shaikh told Reuters Health by email.

"The performance under age 7 seemed ok, but that could just be because of the small numbers of children <7 in our study or due to chance. The results need to be replicated in other studies before its use for children under age 7 could be widely considered," Dr. Shaikh added.

The researchers note that two previous studies have examined accuracy of BinaxNOW. One included a convenience sample of adults, 84% of whom were asymptomatic; the other enrolled a community sample (73% were asymptomatic; 6% were younger than age 18 years).

The reported sensitivities in these studies were in the 89% to 96% range and specificities of >99%; no differences were apparent according to age or presence of symptoms.

The Pittsburgh study, in contrast, included only symptomatic children with suspected COVID-19 and found similar sensitivity (except in those younger than 7 years) but substantially lower specificity.

Differences between results might be due to differences in test interpretation in the previous studies or the differing spectrum of patients included, the researchers say.

"With the use of the BinaxNOW rapid antigen test, one must consider potentially high rates of false-positives and the age of the target population before using it as a stand-alone assay," Dr. Shaikh and colleagues conclude.

The authors say a key strength of the study include determining the test performance in the same setting that it would be used in practice. A key limitation is a lack of cycle-threshold data for the PCR test.

Flawed Conclusion?

In an emailed statement to Reuters Health, Abbott said, "The performance of BinaxNOW in the study is high and is consistent with dozens of other studies we've seen, but the conclusion is flawed."

"BinaxNOW helps prevent outbreaks and stops the disease from spreading in the classroom, which is why it is a critically important tool – especially among children who are unvaccinated," the company said.

"Nearly a year's worth of real-world evidence in hundreds of school districts across the country shows BinaxNOW has been used to keep schools open and children in the classroom. At this point in the pandemic, we should be past the point of relying on studies that ignore the widely accepted science and value of rapid antigen testing," the company added.

The study had no specific funding and the authors have indicated no relevant conflicts of interest.

SOURCE: Pediatrics, online August 30, 2021.