CO 23: Prior Payer Adjustment
A prior payer already adjusted this, and that adjustment carries over.
Read the primary EOB first. This is usually the secondary correctly honouring the primary's allowed amount, not a denial.
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What CO 23 means
CO: Contractual obligation. The provider absorbs it and cannot bill the patient.
So the balance cannot move to the patient. Either the appeal recovers it or the practice absorbs it. That makes the appeal decision the whole decision on this line.
The same code, a different prefix. 23 also arrives as OA 23. The reason for the denial is the same. The prefix decides who pays for it, so the next step is not the same. If your remit says OA 23, read that page instead.
Is It Worth Appealing?
Fix and resubmit. This is a correction, not an appeal. Appealing burns the deadline.
Why It Fires
In the order we see it.
The primary payer's allowed amount and adjustments flowed through to the secondary payer.
The primary EOB was not attached, so the secondary could not reconcile the balance.
How to Fix CO 23, Step by Step
Read the primary EOB first. This is usually the secondary correctly honouring the primary's allowed amount, not a denial.
- 1Step 1: Read the remark code. Find the remark code printed next to CO 23 on the 835 or EOB. It says what the payer wants back. The usual ones are MA04.
- 2Step 2: Find the cause. Match the denial to one of the 2 causes in Why It Fires above, and fix that one.
- 3Step 3: Do this. Read the primary EOB first. This is usually the secondary correctly honouring the primary's allowed amount, not a denial.
- 4Step 4: Attach the documentation. The primary payer's EOB, attached to the secondary claim.
The common mistake. Do not appeal this as a denial. In most cases the secondary is behaving correctly and the balance is contractual or patient responsibility.
Free: the Denial Code Appeal Playbook. 53 codes on one sheet: appeal, fix and resubmit, or let it go, and what to attach. Get the playbook
CO 23 description
A prior payer already adjusted this, and that adjustment carries over.
A prior payer already adjusted this, and that adjustment carries over. So the balance cannot move to the patient. Either the appeal recovers it or the practice absorbs it. That makes the appeal decision the whole decision on this line.
This is our plain-English wording, not the official X12 text. X12 asserts copyright over the published descriptions, so we write our own and say what it means for the money rather than restating the code.
Where this comes from. This is our own reading of the code, not the payer's and not a copy of the standards text. We classify it from how these denials actually resolve. Where we are unsure, we say so rather than guessing.
The Remark Code Beside It
The adjustment code says the claim was reduced. The remark code printed next to it says why, and it is the one that tells you what to send back.
| Remark | What it means |
|---|---|
| MA04 | This was billed as a secondary claim and the payer has no record of what the primary did with it. |
Related Codes
Your Questions Answered
What does CO 23 mean?
A prior payer already adjusted this, and that adjustment carries over. Contractual obligation. The provider absorbs it and cannot bill the patient.
Can you appeal CO 23?
Fix and resubmit. Read the primary EOB first. This is usually the secondary correctly honouring the primary's allowed amount, not a denial.
Why does CO 23 happen?
The primary payer's allowed amount and adjustments flowed through to the secondary payer. The primary EOB was not attached, so the secondary could not reconcile the balance.
What documentation wins a CO 23 appeal?
The primary payer's EOB, attached to the secondary claim.
How do I fix a CO 23 denial?
Step 1: Read the remark code. Find the remark code printed next to CO 23 on the 835 or EOB. It says what the payer wants back. Step 2: Find the cause. Match the denial to one cause: The primary payer's allowed amount and adjustments flowed through to the secondary payer. The primary EOB was not attached, so the secondary could not reconcile the balance. Step 3: Do this. Read the primary EOB first. This is usually the secondary correctly honouring the primary's allowed amount, not a denial. Step 4: Attach the documentation. The primary payer's EOB, attached to the secondary claim.
Most searched: CO 97 · CO 96 · OA 23 · PR 204 · CO 109 · CO 197 · CO 45 · CO 50
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