It depends on your method...
Direct optical observation =
The appropriate code to report is code 87804, Infectious agent antigen detection by immunoassay with direct optical observation; Influenza. For code 87804, a respiratory sample (eg, throat swab, nasopharyngeal swab, nasal aspirate, sputum) is obtained to perform the rapid test.
Code 87804 is reported twice because two separate, distinct analyses are performed, providing two separate test results, one for influenza virus A and one for influenza virus B, even if it was one test kit. Certain payers may require the use of modifier 59 when the same CPT code is used; alternatively, the payer may require use of the units box on the claim form.