The Test Us at Home study was a collaboration with the FDA, NIBIB’s Rapid Acceleration of Diagnostics (RADx)Tech program, and researchers from the University of Massachusetts Chan School of Medicine.
Participants in the study tested themselves using both antigen and PCR tests every 48 hours for 15 days. First, the researchers evaluated how well the antigen tests could detect the virus the day the infection began, which was the first day the participants tested positive with PCR. An antigen test sensitivity was higher among those with symptoms (60%) compared to those without symptoms (9%).
The performance of the antigen tests improved following serial testing: after 48 hours, the sensitivity increased among both symptomatic participants (92%) and asymptomatic participants (39%). The sensitivity continued to improve after an additional 48 hours (94% among symptomatic participants and 56% among asymptomatic participants).
Next, the researchers wanted to assess how antigen tests might perform in a real-world scenario—that is, when a person starts testing after the infection begins. To do this, they evaluated the performance of antigen tests on specific days after a participant first tested positive with PCR testing. Then, they combined the antigen test data spanning from the day the infection began through the following six days.
Among those with symptoms, the antigen tests’ sensitivity increased from 83% on the first test to 93% on the second test 48 hours later, according to the research paper.
The antigen tests’ sensitivity in people who tested positive without symptoms was lower, but it increased with repeat testing every other day, especially when researchers excluded participants who only tested positive with PCR once over the 15-day period. The sensitivity increased from 39% on the first test to 63% on the second test, and 79% on the third test in people who never developed symptoms, according to the research.
Based on the findings, the FDA updated its guidance last year for authorized uses of rapid antigen tests to recommend repeat testing every other day when users receive a negative result. Users should test at least twice if they have symptoms and three times if they don’t have symptoms.
The FDA also allowed antigen test developers to accept the new guidance and update their product instructions instead of conducting repeat testing themselves.
The clinical study highlighted above was conducted entirely virtually. The antigen and PCR test kits were shipped to participants’ homes and the PCR samples were picked up for lab analysis, the researchers reported in a related paper published in the Journal of Clinical and Translational Science. Participants used smartphones and a study app to enroll, give their consent, record their symptoms, and receive testing reminders.
The clinical study was one of the largest to date to pair rapid antigen testing with PCR testing during the first week of the participants’ infection. Of the 7361 individuals enrolled in the study between late 2021 and early 2022, 492 tested positive for SARS-CoV-2, including 154 who had tested negative and were asymptomatic when the study started. These 154 individuals were included in the final analyses.
