Denial code · group CO
CO-252: The payer needs an attachment or documentation before it will decide the claim
Short answer
CO-252 means the payer has stopped the claim because something has to be attached before it can decide: medical records, an itemized invoice, the primary payer's EOB or a certificate of medical necessity. Nothing has been judged yet. Send the requested documentation through the payer's attachment route with the claim number on every page, then track it so the request does not age into a CO-226 denial.
Look up other codes in the denial code library.
Last reviewed by the Remitwright billing team. Editorial policy
Group CO means contractual obligation: the balance is written off, not billed to the patient. The number is the reason; the two-letter group says who carries the balance.
Remark codes that usually come with CO-252
- N4
- The explanation of benefits from the prior insurer is missing, incomplete or not valid
Common causes
The code requires records on every claim under the payer's policy
Unlisted procedure codes, miscellaneous HCPCS codes, drugs billed with a not-otherwise-classified code, a modifier that signals unusual work, and some high-dollar DME items are set to pend for documentation. The claim was fine; the payer's rule is to look before paying.
The secondary claim went without the primary payer's EOB
A secondary payer cannot work out its share without the primary's allowed amount, paid amount and adjustments. If the 837P did not carry that data and no EOB was attached, the claim pends with N4.
An invoice is needed to price the item
Payers price miscellaneous DME codes, custom items and some drugs from the manufacturer's invoice. Without it there is no fee schedule amount to apply and the claim waits.
The payer needs accident or liability details
A diagnosis that suggests an injury makes the payer ask whether auto, workers' compensation or another liable party should pay first. Until the questionnaire or accident details arrive, the claim pends.
The attachment was sent but never linked to the claim
Records uploaded or faxed without an attachment control number, or without the PWK segment on the claim that tells the payer to expect them, sit unmatched in a queue while the claim pends as if nothing had been sent.
How to fix it and resubmit
- 1
Identify exactly what is being asked for
Read the remark code, the payer's letter or the portal note on the claim. If the request is vague, call provider services with the claim number and ask which document and which submission route the payer wants.
- 2
Send the documentation through the payer's attachment channel
Portal upload, fax to the number on the letter, or the electronic attachment transaction where the payer supports it. Put the claim number, patient name and date of service on each page and include a cover sheet listing the enclosures.
- 3
Resubmit with the attachment indicator when the payer wants them together
Some payers want the claim and the attachment to arrive as a pair: a corrected claim with the PWK segment, a report type and an attachment control number, and the documents sent under that same number through the matching route.
- 4
- 5
How to prevent it
- Attachment rules by payer and code built into the scrubber so unlisted codes, miscellaneous codes, not-otherwise-classified drugs and unusual-work modifiers are held until the documentation is ready
- Secondary claims released only after the primary 835 is posted, with the primary's adjudication populated automatically
- Manufacturer invoices and detailed written orders filed with the DME order at intake, not hunted for after the claim pends
- Trip logs and signatures stored against each NEMT claim so a broker or Medicaid plan request can be answered the same day
A CO-252 on a miscellaneous DME code
A DME supplier bills a miscellaneous HCPCS code for a custom wheelchair component. The claim returns CO-252; the payer prices that code from the manufacturer's invoice and wants the detailed written order with it. The biller uploads both through the payer portal with the claim number and a cover sheet. The claim is reprocessed and priced from the invoice. The supplier adds a scrubber hold for miscellaneous codes so the invoice and order go out with the first claim. This is a hypothetical example.
Official text: the X12 claim adjustment reason code list. The meaning above is our paraphrase for billers; the list is the authority.
FAQ
Questions about CO-252
Is CO-252 a denial?
How long do I have to respond to a CO-252?
Should I attach records to every claim to avoid CO-252?
Can I send attachments electronically?
Does a CO-252 affect timely filing?
Next step
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While you wait: see the sample weekly report or read how to work claim denials. You can also download the sample weekly report (PDF).