CO 55: Experimental or Investigational
Treated as experimental or investigational.
Appeal with literature and the payer policy. Low win rate; triage by dollar value.
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What CO 55 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. 55 also arrives as PR 55. 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 PR 55, read that page instead.
Is It Worth Appealing?
Winnable with a clinician. Recoverable on the merits, but somebody clinical has to attest.
How to Appeal CO 55, Step by Step
Appeal with literature and the payer policy. Low win rate; triage by dollar value.
- 1Step 1: Read the remark code. Find the remark code printed next to CO 55 on the 835 or EOB. It says what the payer wants back.
- 2Step 2: Take the first action. Appeal with literature and the payer policy. Low win rate; triage by dollar value.
- 3Step 3: Send the appeal before the deadline. Send it to the payer with the claim, the denial and the documentation, inside the payer's appeal window. See what an appeal letter must contain and the filing limits by payer.
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 55 description
Treated as experimental or investigational.
Treated as experimental or investigational. 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.
Your Questions Answered
What does CO 55 mean?
Treated as experimental or investigational. Contractual obligation. The provider absorbs it and cannot bill the patient.
Can you appeal CO 55?
Winnable with a clinician. Appeal with literature and the payer policy. Low win rate; triage by dollar value.
How do I appeal a CO 55 denial?
Step 1: Read the remark code. Find the remark code printed next to CO 55 on the 835 or EOB. It says what the payer wants back. Step 2: Take the first action. Appeal with literature and the payer policy. Low win rate; triage by dollar value. Step 3: Send the appeal before the deadline. Send it to the payer with the claim, the denial and the documentation, inside the payer's appeal window.
Most searched: CO 97 · CO 96 · OA 23 · PR 204 · CO 109 · CO 197 · CO 45 · CO 50
How Much of This Is Sitting in Your Write-Off Pile?
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