'Not Medically Necessary' Denial: How to Appeal

What This Means

Medicare pays only for care that is “reasonable and necessary” for diagnosing or treating illness or injury — the coverage standard set by Section 1862(a)(1)(A) of the Social Security Act — and a reviewer decided the paperwork submitted with this claim didn’t prove your service met it. On your MSN or EOB the denial usually appears as CARC code CO-50, “these are non-covered services because this is not deemed a ‘medical necessity’ by the payer.” The denial turns on what was documented, not on whether you truly needed the care. Act now: call your doctor’s office and ask for a letter of medical necessity — then file your appeal within 120 days of receiving your MSN (Original Medicare) or 65 days of the date on your denial notice (Medicare Advantage). Your MSN prints your exact filing deadline; use that date if you are close to the line.

Not sure this is your situation? “Not medically necessary” is broad wording that covers several distinct denials:

• Told coverage ended because you’ve stopped improving or “plateaued”? Medicare is not supposed to deny solely for lack of improvement — see maintenance care and the Jimmo settlement.
• Was the treatment called experimental or investigational? That’s a different denial with its own evidence path — see experimental or investigational.
• Was the problem how many visits, not whether the care was needed at all? See too many visits.

A medical necessity denial doesn’t mean you didn’t need the care. It means the reviewer — often an automated system applying written coverage rules — wasn’t given enough clinical evidence to support it, and thin paperwork loses by default. It’s one of the most common reasons Medicare gives for denying claims, and among the most frequently reversed when appealed with better documentation.

Why This Happens

• The claim lacked supporting documentation. Your provider may not have included enough clinical information explaining why the service was needed for your specific condition.
• The service doesn’t match Medicare’s coverage criteria. Medicare and its contractors publish written coverage policies — National and Local Coverage Determinations — that spell out when a service counts as reasonable and necessary. Your situation may not have matched those criteria based on what was submitted.
• Coding didn’t reflect the severity. The diagnosis codes on the claim may not have fully conveyed how serious your condition was.
• Automated review flagged the claim. Many claims are initially reviewed by computer systems that apply broad rules. A human reviewer may reach a different conclusion.

Should You Appeal?

What To Do Next

1. Mark your deadline. For Original Medicare you have 120 days from the date you receive your MSN to request a redetermination — Medicare presumes you received it 5 days after the date printed on it, and your MSN states the exact deadline on its last page. For Medicare Advantage you have 65 days from the date on your denial notice. Don’t ignore the notice — the clock is already running.
2. Call your doctor’s office. Ask them if they can provide a letter of medical necessity or additional documentation supporting the service. Many providers are familiar with this process.
3. Review your denial notice carefully. It should explain the specific reason Medicare found the service not medically necessary, and it will include instructions for how to appeal.
4. File your appeal. For Original Medicare, you’ll submit a written request for redetermination to the Medicare Administrative Contractor listed on your MSN. For Medicare Advantage, follow the instructions on your denial notice.
5. Keep copies of everything. Make copies of your denial notice, any letters from your doctor, and your appeal request before sending them.

Sources

• CMS: Medicare Coverage Determination Process — Medicare coverage is limited to items and services that are “reasonable and necessary” (Social Security Act §1862(a)(1)(A)); how NCDs and LCDs apply the standard.
• X12: Claim Adjustment Reason Codes (CARCs) — official definition of CO-50.
• Medicare.gov: Original Medicare Appeals — the redetermination process; decisions generally within 60 days.
• CMS: First Level of Appeal — Redetermination by a Medicare Contractor — the 120-day filing deadline and 60-day decision timeframe.
• Medicare.gov: Medicare Health Plan Appeals — the 65-day Medicare Advantage deadline; 30-day pre-service, 60-day payment, and 72-hour expedited decision timeframes.
• KFF: Medicare Advantage Prior Authorization Determinations, 2024 — 7.7% of prior-authorization requests denied; 80.7% of appealed denials overturned; 11.5% of denials appealed.
• CMS: Fee-for-Service Advance Beneficiary Notice (ABN) — the ABN is what transfers potential financial liability to the beneficiary.
• 42 CFR 411.400-411.406 — the limitation-on-liability rules that protect you when no valid ABN was given.
• 42 CFR 422.584 — who may request an expedited Medicare Advantage reconsideration, and its exclusion of requests for payment of services already furnished.
• 42 CFR 422.590 — the Medicare Advantage reconsideration decision deadlines: 30 calendar days for a request for a service or item, 60 calendar days for a request for payment; (f) extends service or item requests only.
• Medicare.gov: Medicare Summary Notice — reading your MSN.

Frequently Asked Questions