CO-252
Often appealableAdditional documentation required
Group CO — Contractual Obligation — an adjustment tied to the contract between the insurer and the provider. You usually cannot be billed for a CO amount.
CO-252 means the claim can't be adjudicated until the payer receives additional documentation — such as medical records, an operative report, or an invoice. It's a request for more information, not a final denial of your care.
It's a Contractual Obligation (CO). It usually resolves quickly once the provider sends exactly what the payer asked for.
Got a CO-252 denial? Our free generator can draft a ready-to-send appeal letter for this denial in a few minutes. Start your appeal →
Why you're seeing CO-252
- The service requires supporting records the payer doesn't have yet.
- An invoice or report was needed for a specific item (for example, certain drugs or devices).
- The payer is reviewing the claim and needs documentation to finish.
Can you appeal it?
Usually resolved simply by submitting the requested documentation — a formal appeal is rarely needed.
What to do next
- 1Read the EOB/remark code to see exactly what documentation is requested.
- 2Ask the provider to send the specific records or reports the payer needs.
- 3Confirm the documentation was received and the claim was reopened.
- 4Escalate to an appeal only if the payer denies the claim after documentation is provided.
Evidence that helps
- Whatever specific record, report, or invoice the payer requested.
Frequently asked questions
Is CO-252 a denial?
Not a final one — it's a request for more information before the payer can decide. Once the provider submits exactly what's requested, the claim is typically reprocessed. No formal appeal is usually needed.
Related guide: How to appeal a “Billing or coding error” denial →
Write your appeal now
Generate a tailored appeal letter, escalation letter, and phone script — free, private, and entirely in your browser.
Other common denial codes
Last reviewed July 18, 2026. Denial-code lists (CARC/RARC) are updated three times a year; we review these explanations against the current list.
Sources & references
These explanations are written in plain language and based on the authoritative sources below. Always confirm the specifics against your own plan documents and denial letter.
- ASC X12 — Claim Adjustment Reason Codes (CARC)
The standards body that maintains the official CARC list (the CO/PR codes), updated three times a year.
- CMS / X12 — Remittance Advice Remark Codes (RARC)
The remark codes (N-/M- codes) that accompany a CARC and give the specific reason for an adjustment.
- HealthCare.gov — Appealing a health plan decision
Official overview of internal appeals and external review rights for Marketplace and most private plans.
- U.S. Department of Labor — ERISA claims & appeals
Governs claim and appeal procedures and deadlines for most employer-sponsored (ERISA) health plans.
- Your state's insurance regulator
State agencies enforce external review and consumer protections; find yours via the NAIC directory.
Important: this is not legal or medical advice.
AppealBrain is a free, self-help tool that helps you draft an appeal letter using the information you provide. We are not a law firm, medical provider, or insurance company, and using this tool does not create an attorney–client relationship. Appeal rules and deadlines vary by plan and state — always review your own denial letter and plan documents, and consider consulting a licensed professional for your specific situation. We do not guarantee any outcome.