When a claim comes back with a CO-252 denial, it usually means the payer hit pause — not stop. The message behind this code is simple: “We need more documentation before we can pay you.” It’s one of the most common yet avoidable denials in healthcare billing. Whether you’re running a surgical practice, imaging center, or therapy clinic, these denials can slow cash flow and increase your accounts receivable days. The good news? With the proper process, you can fix CO-252 denials quickly, prevent them from recurring, and get your payments released without wasting weeks on back-and-forths.

What Does CO-252 Denial Code Mean?

Denial Code CO-252 stands for:

“An attachment or other documentation is required to adjudicate this claim/service.”

In short, the payer couldn’t process your claim because something was missing — usually supporting paperwork, medical records, operative reports, or proof of medical necessity.

This is one of the more frustrating denials because it doesn’t mean your coding or billing was wrong; it means you didn’t send what the payer needed to review and approve payment.

Common Reasons for CO-252 Denials

This denial code isn’t random. It usually pops up due to one of the following situations:

Missing Documentation

You didn’t attach the required documents, like:

• Operative or pathology reports
• Progress notes
• Imaging or lab results
• Consent forms or ABNs (Advance Beneficiary Notices)

Example: If you billed CPT 29880 (knee arthroscopy) but didn’t attach the operative report, Medicare or commercial payers will likely return a CO-252 denial asking for the documentation.

Medical Necessity Proof Missing

Sometimes, payers want proof that a service was medically necessary.
If your claim doesn’t include medical records or the diagnosis doesn’t support the CPT code, they’ll issue a CO-252 denial.

Example: A patient gets an MRI for “headache.” If the documentation doesn’t show neurological symptoms or abnormal findings, the payer might deny it pending medical necessity documentation.

Prior Authorization or Referral Documents Not Sent

Even if you got prior authorization, failing to attach or reference the authorization number can trigger this denial.
For some plans, the system can’t automatically match your claim with the prior authorization — so it flags it as missing documentation.

Modifier or Supporting Form Missing

When using modifiers like -22 (Increased Procedural Service) or -GA (Waiver of Liability Statement Issued), payers require additional justification.
If you forgot to include those, expect a CO-252 denial.

Payer-Specific Notes (Medicare, Medicaid & Commercial)

Different payers handle documentation requirements differently. Here’s what you should know:

Medicare

• CO-252 is common for claims involving medical necessity, DME supplies, and surgical procedures.
• MACs (Medicare Administrative Contractors) often request operative or progress notes before payment.
• If it’s a Medicare Part B claim, the denial will include an Additional Documentation Request (ADR) letter.

Medicaid

• Medicaid plans may require documentation for therapy services, mental health, or home health claims.
• Each state Medicaid plan has its own documentation submission portal — check the EOB (Explanation of Benefits) for instructions.

Commercial Payers (Aetna, UnitedHealthcare, BCBS, Cigna)

• Often triggered when EHR systems don’t transmit attachments properly.
• Some plans (like BCBS) require authorization numbers or chart notes to accompany specific CPT codes (e.g., 95851, 97110, 99205).

How to Fix CO-252 Denial in Medical Billing

Quick context: CO-252 = payer says an attachment or documentation is required to adjudicate the claim. The claim itself might be otherwise correct — the payer can’t approve payment until they get the proof they want.

Below are the steps your billing team should run through every time a CO-252 appears.

Read the EOB/ERA Carefully (Don’t assume)

What to do: Open the EOB or ERA the moment you see CO-252. Read every remark code and payer note. The EOB often states which document is missing or the format the payer prefers.

Why it matters: The payer usually tells you exactly what they need — operative note, echo report, prior authorization, ABN, progress notes, or something else. Resubmitting the claim without the correct item wastes time.

What to look for:

• Specific remark codes (e.g., “attachment required,” “medical record requested,” “prior authorization number missing”)
• A web portal or fax number for sending documents
• Any required cover sheet wording or claim reference number

Example: The EOB might say: “CO-252 — Medical records required for CPT 93306. Submit via portal with Claim ID 12345.”

Identify the Exact Missing Document(s)

What to do: Match the CPT/HCPCS and diagnosis to the typical supporting documents. Pull the right items from the EMR/chart immediately.

Common documents payers request for CO-252:

• Operative/surgery report
• Diagnostic test report (MRI, CT, echo, pathology)
• Progress notes documenting medical necessity
• Prior authorization or referral paperwork
• Signed ABN / patient consent or waiver
• Face-to-face encounter notes (home health, behavioral health, therapy)

Why it matters: Sending irrelevant records (a whole chart dump) slows reviewers and increases the chance of misrouting. Send the requested file(s) only — clearly labeled.

Example match: CPT 27447 (knee replacement) → Operative report + pre-op evaluation + pathology (if tissue removed).

Pull, Redact, and Label the Records

What to do: Extract the precise report(s) from the EMR. Remove unrelated PHI if your payer only needs a clinical excerpt (but don’t remove medical necessity info). Save as PDF and use explicit filenames.

Labeling convention (recommended):
ClaimID_PatientLast_First_CPT_DocumentType_Date.pdf
Example: 12345_Smith_John_93306_EchoReport_2025-07-12.pdf

Why it matters: Clear filenames speed payer matching and reduce “lost attachment” outcomes. Redaction avoids privacy issues if you send more than requested.

Quick checklist before sending:

• Document includes patient name, DOB, date of service, and provider name.
• The report contains clinical findings and documentation of medical necessity.
• Signature/authenticator present if required (e.g., path reports).
• File is legible — no truncated pages or scanned halves.

Choose Correct Submission Method

What to do: Use the payer’s preferred channel:

• Portal upload (best)
• Electronic attachment via clearinghouse (275 / attachment transaction)
• Fax to the payer’s document intake number (if portal unavailable)
• Mail only if the payer instructs

Portals and 275 attachments match records to the specific claim. Faxing without including the claim reference or cover page can result in getting lost.

What to include with the attachment:

• Clear subject or cover sheet: “Resubmission for CO-252 — Claim ID [#] / DOS [date] / Patient [name]”
• Provider NPI and TIN, patient MRN or DOB, original claim number.
• A one-line reason: “Submitting operative report requested on EOB CO-252.”

Sample cover note (for portal or fax):

Resubmission of Claim ID: 12345 (DOS: 2025-07-12) — CO-252 denial. Attached: Operative report and pre-op evaluation for CPT 27447. Provider: Oakview Ortho (NPI: 1234567890). Please apply to claim and advise.

Resubmit Properly

Don’t create a brand new claim. Resubmit or “reopen” the original claim per payer rules and attach the documentation. Use the claim number and the denial remark code in the resubmission.

Sending a duplicate new claim can trigger duplicate payment edits or create confusion. Reference the original claim so the payer can easily match the documents.

• If using a clearinghouse: Select “Attach documentation to denied claim — reference EOB/ClaimID” or similar option.
• If you must mail: Include payment attachment cover and write “Resubmission for CO-252 — attach to claim #” on every page.

Log Everything in a Denial Tracker

What to do: Record the denial in your tracker the minute you start work. Use a structured tracker with columns like:

• Claim ID / Patient / DOS
• CPT / Dx
• Denial Code (CO-252) + remark
• Missing docs identified
• Who pulled the docs (name)
• Submission method (portal/fax/clearinghouse)
• Date sent + reference number
• Follow-up date + outcome/status

Documentation helps if you need to escalate or appeal. It gives you data to spot patterns (problem payers, problem CPTs, staff training needs).

Follow Up and Confirm Receipt

What to do: Confirm the payer received your documents. Use the payer’s document reference or the portal to verify status. If you called, note the representative’s name and reference ID.

What to say on the phone (script):

“Hi, I’m calling about Claim ID 12345 for John Smith, DOS 2025-07-12. We resubmitted the requested documentation for CO-252 on [date] via [portal/fax]. Can you confirm Receipt and tell me whether the claim is in review or needs anything else? My contact is [name & phone].”

Why it matters: Electronic submissions sometimes fail. A confirmation prevents surprises and builds a record for escalation.

Escalate If Payer Doesn’t Act

When to escalate: If the payer confirms Receipt but the claim shows no movement after a reasonable internal turn (e.g., your normal adjudication period), escalate.

How to escalate:

1. Ask for a manager-level review and document the rep’s name.
2. Request a “claims intake” ticket number or reference.
3. If unresolved, file a formal appeal citing CO-252, attach the duplicate records, and write a concise argument for medical necessity.

Appeal language sample:

Appeal for Claim #12345 — CO-252 denied for missing documentation. Attached: Operative report and progress notes demonstrating procedure and medical necessity. Please review and reverse the denial.

Escalation keeps the momentum and prevents stale claims.

Post-Resolution Documentation & AR Closeout

When the payer pays or denies again, update your tracker and the patient account. If the payer pays, post payment, and closes AR.

If the payer denies again for a new reason, create the following action (appeal, patient balance, etc).

Clean records let you run revenue reports and avoid duplicate follow-ups.

Conclusion

CO-252 denials aren’t a sign of bad billing — they’re usually a sign of incomplete documentation. Once you understand what each payer expects, these denials become some of the easiest to overturn. The secret is speed and structure: identify what’s missing, attach it correctly, and track the resubmission. When your billing team builds strong documentation habits and uses payer portals smartly, CO-252 denials turn from cash-flow blockers into quick recoveries.

Think of it like paperwork triage — the faster you respond with the proper attachment, the quicker your claim moves from “pending” to “paid.”

Partner with SwiftCare Billing to Handle CO-252s Before They Happen

At SwiftCare Billing, we don’t just manage denials — we help prevent them altogether. Our billing specialists know payer documentation rules inside and out, from Medicare’s attachment requirements to commercial payer quirks that trigger CO-252 denials.

We integrate payer-specific checklists, track resubmissions in real time, and ensure your claims get paid on the first try.

Contact Our Medical Billing Expert Now