Denial code · CARC 50
CARC 50 (CO-50): not medically necessary, in behavioral health
What CO-50 and PR-50 mean on a behavioral-health remittance, the remark codes that travel with them, how the denial shows up by level of care, and why it is usually appealed rather than rebilled.
By the ClaimParrot editorial team · Who we are · Reviewed · 5 min read · 10 cited sources
Quick answer
CARC 50 means the payer decided the service was not medically necessary under its own criteria and treated it as non-covered. With group code CO the provider absorbs the balance; with PR the patient may owe it, usually only after a valid advance notice. A corrected claim rarely fixes CO-50: answer it with the record, the criteria and an appeal.
| Item | Detail |
|---|---|
| Code | CARC 50 · Active on the X12 list; checked October 14, 2026 |
| Plain meaning | The payer reviewed the service against its criteria, decided it was not medically necessary, and treated the charge as non-covered. |
| Group codes seen | CO (contractual obligation), PR (patient responsibility), OA (other adjustment) |
| Common remark codes | N115, M38, N10, N939 |
| Where it shows up in BH | Intensive outpatient (IOP), Partial hospitalization (PHP), Residential SUD (ASAM levels), ABA therapy, TMS |
| Usual next step | Appeal (or the payer's clinical reconsideration), with records and criteria |
| Related codes | CARC 96, CARC 151, CARC 197, CARC 198 |
What does CARC 50 mean?
CARC 50 is the reason code a payer uses when it treats a billed service as non-covered because, in its judgment, the care was not medically necessary. It is a clinical-judgment denial, not a billing error, so the dispute is about whether the record meets the criteria the payer actually applied.
In behavioral health the criteria are usually a level-of-care set such as LOCUS, ASAM, InterQual, MCG or the payer's own guideline. Group health plans must disclose their MH/SUD criteria on request; the criteria request letter tool drafts that request.
What do CO-50, PR-50 and OA-50 mean for who pays?
The group code in front of 50 says who carries the denied amount. CO means a contract or regulation makes the provider write it off. PR means the patient can be billed, which Medicare allows for this kind of denial only when a valid advance notice was signed first. OA needs its remark code to interpret.
| Group + reason | What it signals | Who usually carries the balance |
|---|---|---|
| CO-50 | Provider liable under contract or regulation | Provider; do not bill the patient |
| PR-50 | Patient liable, usually after a signed advance notice | Patient, if that notice was valid |
| OA-50 | Neither CO nor PR applied | Unclear: read the remark code first |
Which remark codes come with CARC 50?
Remark codes narrow the reason. These are the ones most often paired with 50 on behavioral-health remittances; payers can use others.
| Remark code | What it adds | What to check |
|---|---|---|
| N115 | The decision rests on a Local Coverage Determination (LCD), the Medicare contractor's coverage policy. | The LCD and its billing article: covered diagnoses, frequency and documentation rules |
| M38 | The patient is responsible because they were told in writing before the service that the payer would not pay, and they agreed. | That the signed notice is on file and was valid for this service |
| N10 | The payment was adjusted after review by a review organization, a professional consultant, a medical advisor or a peer reviewer. | Who reviewed the case and in what specialty; request the review notes |
| N939 | The payer invites you to request a peer-to-peer review (added to the RARC list in July 2026). | The window to schedule the peer-to-peer call |
Where does CARC 50 show up in behavioral health?
In behavioral health, CO-50 clusters where intensity and duration get reviewed: IOP and PHP days, residential and inpatient continued stays, ABA hours and TMS courses. The pattern repeats: the reviewer says a lower level of care would be safe, or that the record does not show the patient still needs this one.
| Care setting | Typical trigger | Check first |
|---|---|---|
| Intensive outpatient (IOP) | Reviewer says weekly outpatient therapy would meet the need; hours or attendance below the program minimum | Daily notes with hours, current risk and functional impairment |
| Partial hospitalization (PHP) | Record does not show why IOP is not enough | Physician certification, daily structure, failed step-down attempts |
| Residential SUD (ASAM levels) | Continued stay denied because dimension ratings look stale or improved | The latest ASAM assessment by dimension, nursing and incident notes |
| ABA therapy | Requested hours not tied to goals or progress data | Treatment plan, standardized measures, caregiver training notes |
| TMS | Course or diagnosis outside the payer policy or LCD | Medication-trial history and depression rating scales |
Corrected claim, reconsideration or appeal: which fits CARC 50?
Appeal, in most cases. CO-50 is a clinical judgment, so resubmitting the same claim does not reopen it. Rebill only if the line itself was wrong, such as the level-of-care code, diagnosis or hours. Some commercial payers, Aetna among them, send medical-necessity disputes straight to the appeal level.
- 01Confirm the line: dates, units, level-of-care code and diagnosis match the record and any authorization. If they do not, a corrected claim is the right tool.
- 02Request the criteria and the reviewer's rationale, and book a peer-to-peer if the payer offers one (how to prepare).
- 03File inside the window in the notice: at least 180 days for ERISA plans, 60 days for Medicaid managed care and Medicare Advantage, 120 days for Medicare redetermination.
What evidence resolves a CARC 50?
Answer the reviewer's criteria point by point with records from the denied dates. A strong CO-50 packet shows current severity, why a lower level of care would fail, and the treating clinician's reasoning, tied to the payer's own guideline rather than general statements.
- The denial notice and the exact criteria and version applied
- An assessment matching those criteria, dated near the denied days
- Progress notes for each denied date: attendance, hours, response
- Risk records: safety plans, incidents, withdrawal scales, medication changes
- A treating-clinician letter that ties the record to each criterion
How do Medicare, Medicaid and commercial plans differ on CARC 50?
The criteria, the liability rules and the clock all change with the program. Medicare applies national and local coverage policies and the advance-notice rules; Medicaid managed care allows one plan appeal before a state fair hearing; employer plans follow ERISA and the parity disclosure rules.
| Program | What differs |
|---|---|
| Medicare (Original) | NCDs and LCDs apply. The patient is liable only with a valid ABN (modifier GA; GZ means none). IOP needs a physician certification of at least 9 hours a week; PHP at least 20, recertified at least every 30 days. |
| Medicaid managed care | One plan appeal within 60 days of the notice, then a state fair hearing. States often set the criteria, such as ASAM. |
| Commercial and ERISA plans | At least 180 days to appeal; the notice must cite the plan provision and any guideline used. External review generally follows a final internal denial. |
CO-50 on six IOP days
A fictional program billed S9480 for six IOP days for an adult with major depressive disorder. All six lines came back CO-50 with N10, and the letter said weekly therapy would meet the patient's needs.
The biller confirmed the codes, hours and authorization matched, so rebilling would change nothing. The UR lead requested the criteria, booked the peer-to-peer and built the appeal around two facts the rationale ignored: a failed step-down a month earlier and rating scores that had not improved. The psychiatrist reviewed and signed the letter.
Names, dates, payers and amounts are invented for illustration.
What a ClaimParrot packet does here
- When CARC 50 needs an appeal rather than a corrected claim, an appeal packet answers the payer's stated reason.
- A person checks every packet: $29, or $99 for level of care, and the first is free (pricing).
- No remittances, records or PHI are sent: just the reason and a de-identified summary (Trust & security).
Every draft is reviewed and approved by your team. ClaimParrot does not make medical-necessity determinations or give legal advice.
Frequently asked questions
Can we bill the patient for a CO-50 denial?
Not while the group code is CO, which puts the amount on the provider. With PR-50, first check the notice behind it; Medicare requires an ABN signed before the service.
Is CO-50 the same as CO-96?
No. CARC 96 marks a non-covered charge and needs a remark code to say why, often a benefit exclusion. CARC 50 is a medical-necessity judgment, argued from the record and criteria.
Does a peer-to-peer replace the CO-50 appeal?
No. A peer-to-peer is an informal call, and the written appeal deadline keeps running while you wait for it. Book it early and note what the reviewer says.
What if the payer will not say which criteria it used for the CO-50?
Ask in writing. ERISA denial notices must identify any internal guideline relied on, and group plans must disclose MH/SUD criteria on request. Keep the request and any silence in the appeal file.
Primary sources and references
- Claim Adjustment Reason Codes (CARC) code list · X12 · checked
- Remittance Advice Remark Codes (RARC) code list · X12 · checked
- Medicare Claims Processing Manual, Chapter 30, §120.4: limitation-on-liability remark codes · CMS · checked
- MLN006266, Medicare Advance Written Notices of Non-coverage (May 2025) · CMS Medicare Learning Network · checked
- MLN1986542, Medicare & Mental Health Coverage (March 2026) · CMS Medicare Learning Network · checked
- 29 CFR 2560.503-1: ERISA claims procedure · eCFR · checked
- 29 CFR 2590.712: mental health parity, including criteria disclosure in paragraph (d) · eCFR · checked
- 42 CFR 405.942: time frame for a Medicare redetermination request · eCFR · checked
- 42 CFR 422.582: requesting a Medicare Advantage standard reconsideration · eCFR · checked
- 42 CFR 438.402: Medicaid managed care grievance and appeal system · eCFR · checked
General information, not legal or medical advice. Payer rules change; confirm deadlines and requirements in the notice and the plan documents. Read our editorial policy.
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