Reference · 33 codes
Denial code lookup for behavioral health
Type the code the way your remittance prints it. Each page quotes the official X12 description, explains what the code usually means for residential, PHP, IOP, outpatient, and ABA claims, and says whether to correct and resubmit or appeal.
33 codes, with what each means for behavioral health claims
Authorization
- CO-197: The payer found no authorization on file for this service, or none it could match to the claim.
- CO-198: An authorization exists, but the service went beyond it: more days, units, or visits, or dates past the approved span.
- CO-15: Retired.CARC 15 was deactivated on May 1, 2018. Payers on the current X12 list report the same problem with other codes.
- M62: The authorization number on the claim is missing, incomplete, or not one the payer recognizes.
- N54: An authorization exists, but something on the claim doesn't match what it approved.
Medical necessity & level of care
- CO-50: The payer decided the service wasn't medically necessary under the criteria it applied.
- CO-150: The payer thinks the documentation supports a lower level or intensity of service than the one billed.
- CO-151: The payer thinks the documentation doesn't support this many services, or services this often.
- CO-152: The payer thinks the documentation doesn't support how long the service lasted.
- CO-56: The payer classifies the treatment as unproven, experimental, or investigational for the diagnosis billed.
Coding & billing
- CO-16: Something is missing or wrong on the claim itself, and the remark code on the line says what.
- CO-A1: A generic denial. X12 requires a remark code alongside it, and that remark code carries the actual reason.
- MA130: The claim couldn't be processed. There's nothing to appeal; send a new claim with the corrected information.
- CO-4: The modifier on the line doesn't fit the procedure code, or a modifier the payer requires is missing.
- N822: A modifier the payer requires for this procedure code isn't on the line.
- CO-5: The procedure code, or the type of bill, doesn't fit the place of service on the claim.
- CO-11: The diagnosis on the claim doesn't support the procedure billed, under the payer's rules.
- CO-97: The payer counts this service as already paid for inside another service it processed.
- CO-199: On a facility claim, the revenue code and the procedure code on the same line don't match under the payer's rules.
- CO-236: A National Correct Coding Initiative edit says these two codes, or code and modifier combinations, don't go together on the same day.
- CO-B15: The payer won't pay this service until a qualifying primary service has been received and paid.
- N846: The drug's National Drug Code on the claim doesn't correspond to the HCPCS or CPT code billed for it.
Coverage & benefits
- PR-204: The service isn't covered under the patient's current benefit plan, and the PR group code assigns the amount to the patient.
- CO-119: The plan says the member has used up the benefit limit for this time period or occurrence.
- CO-109: This payer isn't responsible for the service, and the claim has to go to the payer that is.
Eligibility & coordination
Provider & credentialing
Filing, records & duplicates
- CO-29: The payer received the claim after its filing deadline.
- CO-226: The payer asked the provider for information and didn't receive it, didn't receive it in time, or found it incomplete.
- CO-252: The payer won't decide the claim until it gets supporting documentation.
- OA-18: The payer already has this exact claim or service line.
How to read a denial line
A denied line on an 835 remittance carries a group code, a claim adjustment reason code (CARC), and often one or more remittance advice remark codes (RARC). The CARC says why the amount was adjusted, the remark code adds detail, and the group code says who carries the amount. Remark codes marked “Alert” are informational only.
| Group | Meaning | What it means for you |
|---|---|---|
| CO | Contractual obligationA contractual agreement or regulatory requirement produced the adjustment. Generally the provider's write-off; not billed to the patient. | A contractual agreement or regulatory requirement produced the adjustment. Generally the provider's write-off; not billed to the patient. |
| PR | Patient responsibilityThe amount may be billed to the patient, subject to your financial agreement and estimate rules. Check the verification record first. | The amount may be billed to the patient, subject to your financial agreement and estimate rules. Check the verification record first. |
| OA | Other adjustmentUsed when no other group applies. The remark code and the contract decide who is liable. | Used when no other group applies. The remark code and the contract decide who is liable. |
| PI | Payer-initiated reductionThe payer considers the amount not the patient's responsibility, but no contract with you supports it, as with a medical-review reduction. | The payer considers the amount not the patient's responsibility, but no contract with you supports it, as with a medical-review reduction. |
Longer walkthrough: behavioral health denial codes, CARC and RARC explained.
Got a stack of these?
Send us the facts on five recent denials — codes, payer, level of care, and dollar amount, no patient information — and we’ll send back five appeal drafts within a week, free. Anything that should be corrected rather than appealed, we’ll say so.
Official descriptions quoted from the X12 Claim Adjustment Reason Codes and Remittance Advice Remark Codes lists, checked September 21, 2026. Group code meanings follow the Medicare Claims Processing Manual, Chapter 22. Payer rules vary; your contract and the payer’s manuals control.