Please correct me if I am wrong, but IgG and IgM are for antibodies. USA is requiring antigen or NAAT (below I took excerpts of interest added below the link).
This is the source – CDC in USA
https://www.cdc.gov/quarantine/pdf/global-airline-testing-order_2021-01-2_R3-signed-encrypted-p.pdf
Test Results must state:
the test result states “NEGATIVE,” “SARS-CoV-2 RNA NOT DETECTED,” “SARS-CoV-2 ANTIGEN NOT DETECTED,” or “COVID-19 NOT DETECTED.” A test marked “invalid” is not acceptable
Negative Pre-departure Test Result for COVID-19 or negative Qualifying Test result means documentation of a negative COVID-19 test taken within the 3 calendar days preceding a flight’s departure. Such documentation may be in paper or electronic format as required by this Order. Testing must be performed using a
viral test. The documentation must also include sufficient verification information—such as the
name and contact information for the laboratory or healthcare personnel who performed the test.
Viral test means a viral detection
test for current infection (i.e., a nucleic acid amplification test or a viral antigen test) approved or authorized by the relevant national authority for the detection of SARS-CoV-2.
