What is the CO 252 denial code?

CO-252 means the payer needs an attachment or other documentation before it can decide the claim. CO is the Contractual Obligation group, so you can't bill the patient while it's unresolved. A remark code on the same remittance says which document is needed.

What is the CO-252 denial code description?

The X12 text for CARC 252 is "An attachment/other documentation is required to adjudicate this claim/service. At least one Remark Code must be provided (may be comprised of either the NCPDP Reject Reason Code, or Remittance Advice Remark Code that is not an ALERT)."

What documents should a therapist send for CO-252?

Whatever the remark code names, for the dates of service on the claim. That's usually the progress notes, the current treatment plan and sometimes the intake assessment. Psychotherapy notes kept separately from the record need the client's authorization under HIPAA and shouldn't go in a routine claim response.

What is the difference between CO-252 and CO-16?

CO-16 is for a claim that lacks information or has a billing error. X12's usage note says CARC 16 isn't for attachments or other documentation. When the payer needs a record, it should use CARC 252.

CO-252 Denial Code: Attachment or Documentation Needed

CO-252 at a glance

	CO-252
Group code	CO, Contractual Obligation (X12)
CARC 252 text (X12)	An attachment/other documentation is required to adjudicate this claim/service. At least one Remark Code must be provided (may be comprised of either the NCPDP Reject Reason Code, or Remittance Advice Remark Code that is not an ALERT).
In the X12 list since	September 30, 2012. Last modified June 2, 2013
What it means for a therapy practice	The claim is on hold or denied until the payer gets a record from you
Who owes the balance	No one yet. Under CO, you can't bill the client while it's open
Usual fix	Read the remark code, send exactly that document with the claim number, and track the deadline

CO 252 denial code description, in plain words

The X12 text above has two parts. The first says the payer needs documentation to adjudicate, meaning to make a decision. The second says the payer must send at least one remark code with it. So a CO‑252 line on its own is incomplete: look on the same line, or in the claim‑level remarks, for the RARC that names the missing piece.

CO‑252 is the code X12 intends for this. The usage note on CARC 16, the general "lacks information" code, says not to use 16 for claims attachments or other documentation. So when the problem is a missing record rather than a missing claim field, the payer should send 252, not 16.

Remark codes you'll see with CO-252

RARC	X12 text	What to send for a therapy claim
N706	Missing documentation.	Call or check the portal. This code doesn't say which record
N710	Missing notes.	The progress notes for the dates of service on the claim
M127	Missing patient medical record for this service.	The record for that date: the progress note, plus the treatment plan in effect

Older guides often list N29 or N225. X12 stopped both on March 1, 2016, after approving more specific codes such as N706 and N710. If a payer still sends N29, ask what it wants.

What to send, and what not to

A payer asking for therapy records almost always wants the clinical record: the intake assessment, the treatment plan and the progress notes with start and stop times. Those are what show the service happened and was medically necessary.

Psychotherapy notes are a separate thing under HIPAA. 45 CFR 164.501 defines them as a mental health professional's notes on the content of a session, kept separate from the rest of the record. The definition leaves out session start and stop times, modalities and frequencies of treatment, test results, and any summary of diagnosis, functional status, treatment plan, symptoms, prognosis or progress. Under 45 CFR 164.508, disclosing psychotherapy notes needs the client's authorization except in narrow cases. A payer request for records is not a reason to send them.

If your progress notes are thin and the real detail lives in separate process notes, CO‑252 requests will keep hurting. Put the clinical summary in the progress note. Our therapy progress report template and the progress notes template show what belongs there.

How to fix CO-252

Find the remark code on the remittance and write down exactly what it asks for.
Check the payer's letter or portal for a request with a deadline and a reference number.
Pull only the records for the dates of service on the claim, and send them through the channel the payer names, with the claim number on every page or on the cover sheet.
If the payer has already closed the claim, send the records with a reconsideration or resubmission, following its rules.
Set a follow-up for two to three weeks later and call if nothing has changed.

CO-252 vs CO-226 and CO-16

Code	When it's used
CO-252	The payer needs an attachment or other documentation to decide the claim
CO-226	The payer already asked the billing or rendering provider for information, and it didn't arrive in time or was incomplete
CO-16	The claim itself is missing information or has a billing error. X12 says not to use it for attachments
PR-227	The payer asked the patient or insured for information and didn't get it

So a CO‑252 that you ignore can turn into a CO-226 on the next pass. Answer the first request. When the payer is waiting on the client instead, you'll see PR-227.

Related therapy codes payers ask records for most often: 90791, 90837 and 90846. If you'd rather have progress notes that already carry the start and stop times, plan and progress a reviewer looks for, Twofold writes them from the session.

Checked against the X12 Claim Adjustment Reason Code and Remittance Advice Remark Code lists on October 19, 2026. CARC 252 was last modified on June 2, 2013, and nothing about it changed this year.

Sources

X12, Claim Adjustment Reason Codes, CARC 16, 226, 227 and 252, checked October 19, 2026.
X12, Remittance Advice Remark Codes, N706, N710, M127, N29 and N225, checked October 19, 2026.
X12, Claim Adjustment Group Codes, checked October 19, 2026.
45 CFR 164.501, definition of psychotherapy notes, checked October 19, 2026.
45 CFR 164.508(a)(2), authorization for psychotherapy notes, checked October 19, 2026.

FAQ

Frequently asked questions

What is the CO 252 denial code?

CO‑252 means the payer needs an attachment or other documentation before it can decide the claim. CO is the Contractual Obligation group, so you can't bill the patient while it's unresolved. A remark code on the same remittance says which document is needed.
What is the CO-252 denial code description?

The X12 text for CARC 252 is "An attachment/other documentation is required to adjudicate this claim/service. At least one Remark Code must be provided (may be comprised of either the NCPDP Reject Reason Code, or Remittance Advice Remark Code that is not an ALERT)."
What documents should a therapist send for CO-252?

Whatever the remark code names, for the dates of service on the claim. That's usually the progress notes, the current treatment plan and sometimes the intake assessment. Psychotherapy notes kept separately from the record need the client's authorization under HIPAA and shouldn't go in a routine claim response.
What is the difference between CO-252 and CO-16?

CO‑16 is for a claim that lacks information or has a billing error. X12's usage note says CARC 16 isn't for attachments or other documentation. When the payer needs a record, it should use CARC 252.

CO-252 Denial Code: Missing Documentation or Attachments