This is a great question!!
Per Medicare Guidance:
Question: What code should we use to bill Medicare if new types of COVID-19 tests are created in the future? Answer: The appropriate code to use would be HCPCS Code U0002 for COVID-19 test methods that are not specified by either U0001 or 87635. CMS will continue to monitor the types of COVID-19 testing methods and adjust coding as necessary depending on the methodology.
Per the FDA:
According to the FDA, positive results from antigen tests are highly accurate, but there is a higher chance of false negatives, so negative results do not rule out infection. Therefore, negative results from an antigen test may need to be confirmed with a PCR test.
Hope that this helps!