MA100 remark code

Remittance advice remark code MA100. Remark codes add detail to the reason code on the same claim line.

Missing or invalid date of current illness

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 MA100 means

The date the current illness, injury or symptoms began is missing, incomplete or not valid.

Some services and claim types require the onset date of the illness or injury. This remark says that date was missing, invalid, or did not make sense with the dates of service.

It usually comes with reason code 16. Check the payer's rules on which services need the date.

Common causes

• The onset date was left blank for a service that requires it.
• The onset date was after the date of service.
• The date was entered in the wrong claim field or with a wrong qualifier.

What to do next

1. Find the onset date in the medical record.
2. Enter it with the correct qualifier on the claim.
3. Send a corrected claim that carries the onset date.

Related codes

• 16 (reason code) Missing information or billing error
• MA31 (remark code) Missing or invalid billing period dates