Who Decides What's Medically Necessary on Medicare: Your Doctor or Your Plan?

Based on 2,013 answers from licensed Medicare agents responding to 17 related consumer questions about medical necessity, prior authorization, denials, and appeals on Medicare Agents Hub.

Your doctor says you need a knee replacement. You've done the imaging. You've tried the injections. The surgeon is ready to schedule.

Then someone from your plan calls and says: not so fast.

If you've been through this, you already know the frustration. If you haven't, it catches people completely off guard. The question underneath it all is the one nobody answers clearly: who actually gets to decide what care you receive on Medicare?

Your doctor decides what treatment to recommend. Original Medicare or your Medicare Advantage plan decides whether the service meets its coverage and medical-necessity rules. If coverage is denied, you generally have the right to appeal.

Two decisions and one safeguard

There are 2 decisions and one safeguard built into every Medicare coverage question.

Your doctor recommends what care is clinically appropriate. They examine you, know your history, and recommend treatment based on what they believe will help. That's the clinical decision.

Original Medicare or your Medicare Advantage plan determines whether the service meets its coverage rules. It reviews whether the recommended care qualifies as "medically necessary" under Medicare's national and local coverage determinations and (for MA plans) additional plan-level guidelines.

If those two decisions conflict, you have the right to appeal. That's the safeguard. And it matters, because the clinical recommendation and the coverage decision don't always line up.

Agents on Medicare Agents Hub describe this split in consistent terms. The doctor determines the care. The plan determines the coverage. The gap between those two decisions is where the real confusion lives.

Why the same surgery works differently on Original Medicare vs. Medicare Advantage

On Original Medicare with a Medigap supplement, most services do not require prior authorization, although Medicare applies coverage and medical-necessity rules and requires advance review for certain services and equipment. If Medicare covers the service, a Medigap policy may pay some or most of the applicable deductibles and coinsurance, depending on the policy.

On a Medicare Advantage plan, a private insurance company is the primary payer. That company may require prior authorization before the surgery happens. Your surgeon's office submits documentation. The plan reviews it. And sometimes the plan says no, or requires documentation that conservative treatments (such as physical therapy) were attempted first, or says the surgeon isn't in their network.

Agents describe this contrast repeatedly across hundreds of answers. On Original Medicare, the doctor's recommendation and payment authorization are closely linked. On Medicare Advantage, they can diverge, sometimes significantly.

To be clear: Medicare Advantage plans are required by CMS to cover everything Original Medicare covers. The difference isn't what they cover on paper. It's how they approve it and when.

What "prior authorization" actually means when your doctor's office says it

Prior authorization is the step where your plan reviews a procedure before it happens to decide whether it meets their criteria for coverage. Your doctor's office submits clinical documentation. The plan reviews it. Then they approve, deny, or request more information.

For many people, this is the first time they realize their plan has a say in what care gets paid for. Agents report that prior authorization is one of the most common sources of confusion and frustration among their clients, especially those who switched from employer coverage or from Original Medicare to an Advantage plan.

Some things to know about prior authorization:

• Many Medicare Advantage plans require prior authorization for certain surgeries, advanced imaging, post-acute care and other services. The exact requirements vary by plan.
• Original Medicare generally does not require prior authorization, though CMS has prior-authorization and pre-claim-review programs for certain procedures, equipment and other categories. The WISeR pilot program, operating in 6 states during 2026, adds requirements for specific services.
• A prior authorization request is not a denial. HHS Office of Inspector General reports show that MA organizations approve the vast majority of requests, though they also issue millions of denials, some of which do not comply with Medicare coverage rules.
• The provider usually submits the clinical information, but you should verify that the request was submitted and follow up on its status.

Beginning January 1, 2026, affected payers generally must issue prior-authorization decisions within 72 hours for expedited requests and 7 calendar days for standard non-drug requests.

When a claim gets denied: what actually happens next

A denial means Medicare or the plan determined that it would not cover or pay for the requested service. The reason may involve medical necessity, missing documentation, network rules, authorization requirements or another coverage issue. Agents are emphatic on one point: a denial is not the final word.

The appeals process has 5 levels, and agents say most people give up too early. The process differs depending on whether you have Original Medicare or a Medicare Advantage plan.

If you have Medicare Advantage

1. Reconsideration by your plan: you generally have 65 calendar days from the denial notice to file
2. Review by the Part C Independent Review Entity: if the plan upholds the denial, it automatically forwards the case to an outside reviewer
3. OMHA hearing or review: if the amount in question reaches the threshold ($200 in 2026)
4. Medicare Appeals Council review
5. Federal District Court review: if the separate judicial threshold is met

If you have Original Medicare

1. Redetermination by the Medicare Administrative Contractor
2. Reconsideration by a Qualified Independent Contractor
3. OMHA hearing or review
4. Medicare Appeals Council review
5. Federal District Court review

The fact that an independent reviewer exists is something agents wish more people knew about. Your plan doesn't get the last say. An outside entity does.

For a full walkthrough of the process, see our guide on how to appeal a denied Medicare claim.

Peer-to-peer review

Some Medicare Advantage plans and review programs allow the treating clinician to request a peer-to-peer discussion with a plan medical reviewer. This means your physician speaks directly with a medical director to make the case for why the treatment is necessary.

Because availability and deadlines vary, the provider should check the denial notice and the plan's procedures promptly. A peer-to-peer discussion may help resolve the issue without completing every formal appeal level. If your doctor's office hasn't mentioned it after a denial, ask them about it.

Where an agent can help (and where they can't)

Licensed Medicare agents can't override a plan's denial. They can't call the insurance company and demand approval. But agents describe their role in this process in practical terms:

• Plan selection: An agent who understands your health situation can help compare plans' networks, authorization rules and coverage trade-offs. This is where the MA-vs-Medigap conversation matters most.
• Explaining the process: Many people don't know they can appeal, don't know about peer-to-peer review, and don't know the timeline. Agents fill that gap.
• Connecting you with resources: Agents can point you to your plan's member services, your State Health Insurance Assistance Program (SHIP), or 1-800-MEDICARE.
• Annual plan review: If your current plan is routinely denying or delaying care your doctors recommend, that's a signal to review your options during the next enrollment period.

One thing agents consistently emphasize: the right time to think about medical necessity decisions is before you pick a plan. Once you're in the middle of a denial, your options are limited to the appeals process.

The AI-denial question agents are raising

A growing number of agents are openly concerned about Medicare Advantage plans using algorithmic or AI-driven systems to process prior authorization requests and claim reviews.

Some agents believe automated systems are more likely to issue denials than a human reviewer would be. Investigative reporting and congressional scrutiny in recent years have examined how some MA insurers use predictive algorithms to flag claims for denial.

CMS rules require Medicare Advantage plans to apply Medicare coverage requirements and evaluate whether care is medically necessary for the individual patient. Using an algorithm does not allow a plan to disregard those coverage requirements.

Agents are divided on how much weight to give this issue.

Some agents argue that the automation trend is a fundamental problem with Medicare Advantage: that handing coverage decisions to an algorithm removes the human judgment that should be part of medical care, and that the financial incentive for plans to deny claims creates a structural bias.

Other agents push back, saying prior authorization exists across all payer types, that MA plans approve the vast majority of requests, and that the actual process involves multiple review steps with appeal rights built in.

A coverage denial does not necessarily mean the treatment itself is prohibited, but it can make the treatment financially or practically inaccessible. What's not in dispute: if you believe a claim was wrongly denied, you have the right to appeal, and an independent reviewer (not the plan) gets the next look.

What observation status has to do with medical necessity

Observation status is a related example of how medical-necessity and coverage classifications can affect what Medicare pays. You go to the hospital. You're in a bed. You're getting treatment. But the hospital classified you as "under observation" instead of formally admitting you as an inpatient.

This matters because Medicare Part A only covers inpatient stays. Observation is technically outpatient, billed under Part B, with different cost-sharing. And it can disqualify you from Medicare-covered skilled nursing care afterward, which generally requires a 3-day inpatient stay (though some Accountable Care Organizations and Medicare Advantage plans can waive the 3-day requirement).

The medical necessity standard applies here too. The hospital's utilization review team decides whether your condition warrants inpatient admission. If they say no, you're "under observation" even though you're in a hospital bed overnight.

If the hospital first admitted you as an inpatient and then changes you to outpatient observation status, you may have a right to a fast appeal. The hospital should provide a Medicare Change of Status Notice explaining how to request one.

How to protect yourself

Based on what agents recommend across thousands of answers:

1. Know your plan type. If you're on Medicare Advantage, understand that prior authorization is part of the deal. If reducing prior-authorization requirements is a priority, Original Medicare with an available and affordable Medigap policy may be worth comparing with Medicare Advantage. Keep in mind that Medigap availability, premiums and medical underwriting can affect your ability to obtain a policy outside protected enrollment periods. Talk to a local agent about the trade-offs.
2. Ask about prior authorization before scheduling. When your doctor recommends a procedure, ask whether prior authorization is needed and who handles the submission.
3. If you get a denial, don't stop there. Ask your doctor to submit additional documentation. Ask about a peer-to-peer discussion. File a formal appeal. Agents say many denials get overturned when someone pushes back.
4. Keep records. Save every notice, every Explanation of Benefits, every denial letter. You'll need them if you appeal.
5. Review your plan annually. If your plan is creating friction around care your doctors recommend, that's information for your next enrollment decision. Plans change every year, and so do your options.

The medical necessity question is really a trust question. You're trusting your doctor to recommend the right care. You're trusting your plan to pay for it. And when those two disagree, you need to know that the system gives you a path to push back. It takes effort. But the right to appeal exists, and agents say it works more often than people expect.

Frequently asked questions

Who decides whether something is medically necessary for Medicare?

Your doctor decides what treatment to recommend based on your medical history and condition. Original Medicare or your Medicare Advantage plan then decides whether the service meets its coverage and medical-necessity rules. If those two decisions conflict, you have the right to appeal.

Can Medicare Advantage override my doctor?

A Medicare Advantage plan cannot make medical decisions for you, but it can decide not to cover a service if it determines the service doesn't meet the plan's medical-necessity or coverage criteria. If that happens, you can appeal through Medicare's 5-level appeals process, starting with a reconsideration by your plan.

Does Original Medicare require prior authorization?

Original Medicare generally does not require prior authorization for most services, though CMS does have prior-authorization and pre-claim-review programs for certain procedures, equipment, scheduled ambulance services and other categories. The WISeR pilot program, operating in 6 states during 2026, adds requirements for specific services.

Can I appeal a Medicare medical-necessity denial?

Yes. Medicare has a 5-level appeals process for both Original Medicare and Medicare Advantage. The process starts differently depending on your coverage type, but both paths include review by independent entities outside your plan. Many denials are overturned on appeal.

How long does a Medicare Advantage appeal take?

The first level of appeal (reconsideration by your plan) generally requires a decision within 30 days for standard pre-service requests or 60 days for payment requests. Expedited requests must be decided within 72 hours. If the plan upholds the denial, the case automatically moves to an Independent Review Entity for further review.

Official Medicare sources

• Medicare Advantage appeals and reconsideration (CMS.gov)
• Prior authorization and pre-claim review initiatives (CMS.gov)
• Appealing a change in status during a hospital stay (Medicare.gov)
• Skilled nursing facility care coverage (Medicare.gov)

Medicare policy information reviewed July 25, 2026. Individual coverage decisions depend on the service, medical documentation, plan rules and applicable Medicare coverage criteria.