M81 remark code

Remittance advice remark code M81. Remark codes add detail to the reason code on the same claim line.

Code to the highest level of detail

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 M81 means

A diagnosis or procedure code was not reported with the full specificity the code set requires.

The payer is saying the code used is not complete. Many diagnosis codes have more characters below the category level, and billing the shorter form is treated as invalid.

It normally comes with reason code 16 and sometimes with M76. A corrected claim using the complete code fixes it.

Common causes

• A category level diagnosis code was billed when a more specific code exists.
• A required seventh character or laterality detail was left off.
• Codes were copied from an old problem list without updating.

What to do next

1. Ask coding to assign the full code from the documentation.
2. Check that the billing system is not truncating codes.
3. Send a corrected claim with the complete, specific code.

Related codes

• 16 (reason code) Missing information or billing error
• M76 (remark code) Missing or invalid diagnosis code
• MA63 (remark code) Missing or invalid principal diagnosis