False-Positive Test Results More Likely for Women and Patients With Autoimmune Disorders

Many people take at-home rapid antigen tests for COVID-19 due to their quick results and their ability to diagnose infection while limiting the spread of the virus. The number of people who receive a false-positive result with an antigen test is low (less than 1%), which signifies that rapid antigen tests are still accurate. However, of this 1% statistic, women and people diagnosed with an autoimmune disorder were found to make up the majority of the false positives.

The study involved 2 longitudinal cohort studies that featured patients who underwent daily rapid antigen testing and reverse-transcriptase–polymerase chain reaction (RT-PCR) testing for COVID-19. Participants in each study were considered to have a false positive if they tested negative on an RT-PCR test 48 hours after receiving their rapid antigen test results. All the tests included in both studies used anterior nasal samples.

The study took place over 76,610 days and involved 11,297 participants. One hundred ninety-one participants in this report achieved false-positive results, and 13 of the participants had consistently false-positive results, with most of them being women. Patients with persistent false-positive results also had an autoimmune disorder, with 6 out of 13 patients having a diagnosis.

Some researchers theorize that the reason for false-positive results being higher among women and those with autoimmune disorders is because of cross-reactivity between test antibodies with rheumatoid factor. They recommend that patients with a history of false-positive results, an autoimmune disease, and rheumatoid factors should investigate testing out a different brand of rapid antigen test. Investigating the reasons behind false-positive test results can help researchers understand more accurate ways to deliver COVID-19 tests to the public.
 

Reference

Herbert C, McManus DD, Soni A. Persistent false positive Covid-19 rapid antigen tests. The New England Journal of Medicine. 2024;390(8):764-765. doi:10.1056/nejmc2313517