What about units billed? Since its testing for more that one antigen, can we bill 3 times with modifier 59?
No, you can't bill it multiple units. It is one, single test. Read about lab panels in CPT. There might be some rare, if any, occurrence where it was done more than once on the same date. That would require medical necessity documentation and probably a 91, it would be highly unlikely.
Other resources with info, look up your MAC or health plan for more info. Example:
A respiratory pathogen panel test is a single service with a single unit of service (UOS=1). A respiratory pathogen panel test must not be unbundled and billed as individual components regardless of the fact that the panel reports multiple individual pathogens and/or targets.
And for EM, no, it is a single test.
See the AMA CPT definitions.
https://www.ama-assn.org/system/files/2023-e-m-descriptors-guidelines.pdf
Test: Tests are imaging, laboratory, psychometric, or physiologic data. A clinical laboratory panel (eg, basic metabolic panel [80047]) is a single test. The differentiation between single or multiple tests is defined in accordance with the CPT code set. For the purpose of data reviewed and analyzed, pulse oximetry is not a test.
Unique: A unique test is defined by the CPT code set. When multiple results of the same unique test (eg, serial blood glucose values) are compared during an E/M service, count it as one unique test. Tests that have overlapping elements are not unique, even if they are identified with distinct CPT codes. For example, a CBC with differential would incorporate the set of hemoglobin, CBC without differential, and platelet count. A unique source is defined as a physician or other qualified health care professional in a distinct group or different specialty or subspecialty, or a unique entity. Review of all materials from any unique source counts as one element toward MDM.