CO 13 denial code

Claim adjustment reason code 13. Often reported as CO 13.

Patient died before the date of service

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 13 means

The payer's records show a date of death that is earlier than the date of service on the claim.

The payer has a date of death on file for this member that comes before the service date billed. Either the service date is wrong, the payer's death record is wrong, or the wrong patient was billed.

Services billed on the day of death, or after death for certain covered items, may still be payable, so look closely before writing anything off. Group code CO is typical.

Group codes seen with 13

On a remittance, 13 comes after a group code. These are the ones it is most often reported with:

• CO 13 (Contractual Obligation): The provider's side of the ledger. The reduction comes from the payer contract or a rule the provider has to follow, and the patient normally cannot be billed for it.

The payer chooses the group code for each adjustment, so the same reason code can appear with another group code on your remittance. Read the two together. More about group codes.

Common causes

• The date of service on the claim was keyed incorrectly.
• The claim was billed under the wrong patient or member ID.
• The payer has an incorrect date of death on file for the member.

What to do next

1. Check the date of service against the encounter record.
2. Confirm the patient identity and member ID on the claim.
3. Send a corrected claim if a date or identifier was wrong.
4. If the patient is alive, ask the patient or family to have the plan correct its records, then request reprocessing.

Related codes

• 14 (reason code) Patient born after the date of service
• 16 (reason code) Missing information or billing error
• 31 (reason code) Payer cannot identify the patient