MA66 remark code

Remittance advice remark code MA66. Remark codes add detail to the reason code on the same claim line.

Missing or invalid principal procedure

Unofficial reference. This is our own plain-English explanation, not the official code text. Payer rules differ. Verify with the payer and the official X12 code list. AlphaPrefix is not affiliated with X12, CMS or any payer. Data last updated Nov 11, 2026.

What MA66 means

The principal procedure code on an institutional claim is missing, incomplete or not valid.

The payer needs a valid principal procedure on inpatient claims where a procedure was done. This remark says it was blank, invalid for the date, or otherwise unusable.

It usually comes with reason code 16, and a corrected claim is the fix.

Common causes

• The principal procedure code was not entered when one was performed.
• The code was invalid or incomplete for the discharge date.
• The procedure date did not fall within the stay.

What to do next

1. Ask coding to confirm the principal procedure and its date.
2. Check the code against the set in effect for the discharge date.
3. Send a corrected claim with the confirmed principal procedure.

Related codes

• 16 (reason code) Missing information or billing error
• M67 (remark code) Missing or invalid other procedure code
• MA63 (remark code) Missing or invalid principal diagnosis