A medical necessity denial means the payer decided the care was not needed, or not needed at the level you billed. In behavioral health, these usually hit residential, PHP and IOP days, often at concurrent review while the patient is still in care.
These denials are worth fighting. In California, independent reviewers overturned 79% of residential treatment denials in member appeals that reached the state's external review from 2021 to 2026 (DMHC data). That is an upper bound for cases that went all the way, not a forecast for a first appeal.
Key points
- Confirm it is a clinical denial before you write an appeal.
- Map the chart to the criteria the payer named, page by page.
- Track two clocks: the payer's and the member's.
Step 1: confirm what kind of denial it is
| Denial | Codes you may see | Route |
|---|---|---|
| Medical necessity | CO-50 | Clinical appeal, peer-to-peer, then external review |
| Level or length of care | CO-150, CO-151, CO-152, CO-198 | Clinical appeal with records |
| No authorization | CO-197 | Check auth records first; appeal if urgent admission rules apply |
| Billing or coding error | CO-16, CO-4, CO-11 | Corrected claim, not an appeal |
Sending a clinical appeal for a billing error wastes a level of appeal. Sending a corrected claim for a clinical denial changes nothing.
Step 2: act fast on concurrent review denials
When a payer cuts days during the stay, ask for a peer-to-peer review right away. The attending physician talks to the payer's reviewer and walks through the clinical picture. Windows are short. UnitedHealthcare, for example, offers peer-to-peer within 3 business days of an inpatient denial and 21 calendar days for outpatient.
Write down the reviewer's name, the date, the criteria they cited and the outcome. If the denial stands, that record becomes part of your written appeal.
Step 3: build the appeal packet
- The denial letter, with the criteria the payer named (for example The ASAM Criteria or LOCUS)
- A short cover letter: patient, dates, level of care, what you want reversed
- Each criteria dimension matched to chart evidence, with page numbers
- A letter from the treating physician on why this level was needed
- Timeline of care: admission, reviews, step-downs, discharge plan
- Peer-to-peer notes, if one happened
- Proof of timely filing and any authorization numbers
Under the federal ERISA claims rule, a member is entitled to copies of documents relevant to the claim, free of charge, on request. Ask for the reviewer's notes and the full criteria used.
Step 4: know your deadlines
| Who | Published window |
|---|---|
| Employer plans under ERISA (member appeal) | At least 180 days from the denial notice |
| UnitedHealthcare and Optum Behavioral Health | 12 months total for reconsideration and appeal |
| Cigna | 180 calendar days; 365 in California |
| Carelon clinical appeals | Level I within 180 days, Level II within 90 days |
| California DMHC-regulated plans (provider disputes) | No less than 365 days |
Your contract and the member's plan document can set different dates. Use the earliest one that applies.
Step 5: provider appeal or member appeal
A provider appeal runs under your contract. A member appeal runs under the plan and leads to external review. An assignment of benefits is not the same as being the member's authorized representative; UnitedHealthcare says so in writing. Collect a signed authorized representative form at admission so the member route is open when you need it.
After the internal appeal, the next step depends on the plan. California state-regulated plans use Independent Medical Review. Most self-funded employer plans use federal external review instead.
Not legal advice. This guide is general education, not legal advice. Plan documents, provider contracts and state law can change the rules. Talk to a health care attorney about a specific case.
Frequently asked questions
How long do I have to appeal?
It depends on the payer, the contract and the plan. ERISA plans must give members at least 180 days. Payer contracts range from 60 days to 12 months. Check the denial letter first.
Is a peer-to-peer review the same as an appeal?
Usually not. At most payers it is a separate conversation before or alongside the written appeal. If it fails, file the written appeal.
Can a facility file an IMR in California?
The member files, or someone the member designates. California law lets the provider join or assist the member and advocate for them.
What wins medical necessity appeals?
Specific evidence. Match each criteria dimension the payer cited to dated chart entries, and explain why a lower level of care was not safe.
Sources
- California DMHC, IMR determinations data set (CHHS Open Data), 2021 to 2026, recomputed by Sky Gathering RCM (opens in a new tab)
- UnitedHealthcare, Pre- and post-service appeals and reconsiderations (opens in a new tab)
- 29 CFR 2560.503-1, ERISA claims procedure (Cornell LII) (opens in a new tab)
- Cigna Healthcare, Appeals and disputes policy and procedures (opens in a new tab)
- Cigna Healthcare, California dispute resolution policy (opens in a new tab)
- Carelon Behavioral Health, Provider handbook (PDF) (opens in a new tab)
- 28 CCR § 1300.71.38, provider dispute resolution (Cornell LII) (opens in a new tab)
- Cal. Health & Safety Code § 1374.30 (IMR eligibility and deadlines) (opens in a new tab)
- 29 CFR 2590.715-2719, internal claims and appeals and external review (eCFR) (opens in a new tab)
- X12, Claim Adjustment Reason Codes (official list) (opens in a new tab)
Last reviewed October 2026. Payer rules change; check the source before you file.
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