Rapid antigen tests are commonly used in the diagnosis of respiratory pathogens including influenza viruses. Rapid antigen tests perform best when the person is tested in the early stages of infection with SARS-CoV-2 when viral load is generally highest. The FDA cites rapid antigen tests can be used for screening testing in settings in which repeat testing could quickly identify persons with SARS-CoV-2 infection to inform infection prevention and control measures, thus preventing transmission. Further, in such setting, immediate results with antigen tests can be more valuable even though they may have lower sensitivity than PCR tests, especially when rapid turnaround time is required.
The table below highlights some key points of differentiation between PCR and antigen tests.
Summary of Some Differences between RT-PCR Tests and Antigen Tests
| RT-PCR Tests | Antigen Tests | |
|---|---|---|
| Intended Use | Detect Current Infection | Detect Current Infection |
| Analyte Detected | Viral RNA | Viral Antigens |
| Specimen Type(s) | Nasal Swab, Sputum, Saliva | Nasal Swab |
| Sensitivity | High | Moderate |
| Specificity | High | High |
| Test Complexity | Varies | Relatively Easy to Use |
| Authorized for Use at the Point-of-Care | Most devices are not, some devices are | Yes |
| Turnaround Time | Ranges from 15 minutes to > 2 days | Approximately 15 Minutes |
| Cost/Test | Moderate | Low |
Source: Interim Guidance for Rapid Antigen Testing for SARS-CoV2, September 4, 2020
