An antigen test kit sent to nursing homes nationwide last year has some major pluses, despite the potential for false negatives, according to the results of a new study from the Centers of Disease Control and Prevention. 

When compared with real-time polymerase chain reaction (RT-PCR) testing, the BinaxNOW antigen test’s detection of COVID-19 infection (test sensitivity) is 64% for specimens from symptomatic persons and 36% for specimens from asymptomatic persons, CDC researchers reported. But specificity — the detection of no infection — was high for both groups, at almost 100%, reported lead author William A. Bower, M.D., of the CDC’s COVID-19 Response Team.

Administering the test in a lower-prevalence setting likely will result in a lower probability that subjects with positive results have the disease, Bower and colleagues noted. But the test’s high specificity, plus relatively quick turnaround time and lower costs, support its usefulness — especially in situations where there is ongoing testing, they wrote. 

“The faster turnaround time of the antigen test can help limit transmission by more rapidly identifying infectious persons for isolation, particularly when used as a component of serial testing strategies,” they concluded.