MA18 remark code

Remittance advice remark code MA18. Remark codes add detail to the reason code on the same claim line.

Alert: forwarded to supplemental insurer

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 MA18 means

An informational alert that the claim was also sent on to the patient's supplemental insurer for its share.

This crossover remark tells you the payer automatically passed the claim to the patient's supplemental plan. The supplemental insurer should process it without a separate claim from you.

It is an alert, not a denial. Sending your own claim to the supplemental plan as well can create duplicate denials.

Common causes

• The patient's supplemental plan is set up to receive crossover claims.
• The primary payer left a balance such as deductible or coinsurance.
• Crossover information is on file with the primary payer.

What to do next

1. Flag the account as crossed over so a duplicate claim is not sent.
2. Wait for the supplemental remittance within its normal processing time.
3. If nothing arrives, check claim status with the supplemental insurer before resubmitting.

Related codes

• MA07 (remark code) Alert: claim forwarded to Medicaid
• MA08 (remark code) Alert: bill the other insurer yourself
• 18 (reason code) Exact duplicate claim or service