Medicare Prior Authorization: What Original Medicare and Medicare Advantage Require

By Medtransic Team | August 13, 2026 | 11 min read | Updated: August 13, 2026

Quick Summary: Original Medicare requires prior authorization for a short list of services. Medicare Advantage requires it for almost everything. Most of the confusion in a practice comes from treating those two as one payer.

Two Systems Wearing One Name

Ask whether Medicare requires prior authorization and you will get two correct answers that contradict each other. Both are right. They are describing different programmes.

Original Medicare, the traditional fee-for-service programme, requires prior authorization for a short and published list of items and services. Medicare Advantage plans are private plans that administer the Medicare benefit, and they set their own authorization requirements on top of it.

That is the whole source of the confusion. A staff member who learned Medicare on the fee-for-service side under-checks, and one who learned it on a Medicare Advantage panel over-checks.

Prior authorization and pre-claim review are not the same thing

CMS draws the line by timing. Under prior authorization, the decision comes before the service is rendered. Under pre-claim review, you may render the service first and get the decision before you submit the claim. Both end in an affirmed or non-affirmed decision, but only one of them holds up the care.

What Original Medicare Requires

Less than most practices expect. CMS runs five current initiatives across the whole of fee-for-service Medicare, and everything outside them proceeds without an authorization request.

• Prior authorization for certain hospital outpatient department services.
• Prior authorization for certain durable medical equipment, prosthetics, orthotics and supplies on the Required Prior Authorization List.
• Prior authorization for repetitive scheduled non-emergent ambulance transport.
• The Review Choice Demonstration for Home Health Services.
• The Review Choice Demonstration for Inpatient Rehabilitation Facility Services.

The hospital outpatient list is the one that touches the most physician practices, and it has grown in three steps rather than continuously.

Nothing has been added since. That stability is useful, because it means a practice can learn this list once rather than rechecking it every quarter.

There is also a gold carding scheme running inside Original Medicare that gets very little attention. Under a rule CMS issued in December 2025, DMEPOS suppliers who reach a provisional affirmation rate of 90% or higher can be exempted from prior authorization altogether, and the first exemption cycle began on June 1, 2026.

The WISeR Model, Live in Six States

This is the genuinely new development, and it started this year. The Wasteful and Inappropriate Service Reduction Model runs from January 1, 2026 to December 31, 2031 in New Jersey, Ohio, Oklahoma, Texas, Arizona and Washington.

It applies to a narrow set of Original Medicare items and services, with CMS naming skin substitutes, knee arthroscopy for knee osteoarthritis and electrical nerve stimulation as examples. It covers hospital outpatient departments, ambulatory surgery centres, and office and home settings in those states.

• You choose the mechanism, not whether to be reviewed. Submit a prior authorization request, or submit the claim and have it go to pre-payment medical review instead.
• Determinations usually arrive within three days, and within two days for a confirmed expedited request.
• A recommendation not to affirm must be made by a licensed human clinician. Technology alone cannot produce it.
• Peer-to-peer review is available as part of a resubmission, and resubmissions are unlimited.
• CMS says the model does not change Medicare coverage policy or payment rates.

Medicare Advantage Is Where the Volume Is

If a practice feels buried in Medicare prior authorizations, this is why. The private side of Medicare now covers a majority of beneficiaries and requires authorization at a scale the fee-for-service programme does not approach.

• 55% Of eligible beneficiaries in Medicare Advantage - KFF, 2026. 35.2m of 64.2m with Parts A and B
• 99% Of enrollees in plans requiring prior authorization - KFF, 2026
• 4.1m Requests denied, out of nearly 53m submitted - KFF, 2024 data. A 7.7% denial rate
• 80.7% Of appealed denials overturned - KFF, 2024. Only 11.5% were appealed

The requirement is not spread evenly. On the KFF figures, the shares of Medicare Advantage enrollees in plans requiring authorization run at 97% for acute inpatient stays, 95% for skilled nursing, 94% for Part B drugs and 90% for home health, but only 6% for preventive services.

That pattern is worth reading as a map. Authorization pressure sits on expensive, extended and post-acute care, which is also where a delay does the most clinical harm.

Three Rules Practices Underuse

These are all settled, published requirements. They are underused because they are not obvious, not because they are contested.

A missed deadline is a denial you can appeal, not an approval

This one is commonly stated backwards. Federal regulation provides that if a Medicare Advantage organisation fails to give timely notice of an organization determination, that failure is itself an adverse determination and may be appealed.

The practical difference is large. A practice that believes silence means approval will go ahead and deliver the service. The rule says silence means you have been denied and the clock on your appeal has started.

A patient who switches plans mid-treatment gets 90 days

Coordinated care plans must give a minimum 90-day transition period when an enrollee already undergoing treatment moves to a new Medicare Advantage plan. During that period the new plan may not require prior authorization for the active course of treatment.

The same rule requires that an approval for a course of treatment stays valid for as long as the treatment is medically reasonable and necessary. Both are worth naming directly when a plan asks for a fresh request mid-course.

Your payers now have to publish their own numbers

Under the CMS Interoperability and Prior Authorization Final Rule, impacted payers must publicly report certain prior authorization metrics each year on their own website. The first set was due by March 31, 2026.

This is new leverage. Arguing that a plan is slow used to be a matter of impression, and now it is a matter of a figure the plan published itself.

The Appeal Gap

Two numbers from the same dataset deserve to be read together. In 2024, 11.5% of denied Medicare Advantage prior authorization requests were appealed. Of the appeals that were filed, 80.7% were partly or fully overturned.

Nearly nine in ten denials were accepted without challenge, and the small share that were challenged were usually reversed. Whatever else that says about the denials, it says the appeal is worth filing far more often than it is filed.

A Process That Holds Up

Establish which Medicare you are dealing with

Before anything else, confirm whether the patient is in Original Medicare or a Medicare Advantage plan, and if the latter, which one. The answer changes the requirement, the deadline and the appeal route.

Check the requirement against that specific plan

For Original Medicare, check the published lists, plus the WISeR service list if you practise in one of the six states. For Medicare Advantage, check the plan, because the requirement is set by the plan and not by Medicare.

Submit complete, and route urgent cases to expedited review

An incomplete request restarts the clock rather than pausing it. Where a delay would jeopardise the patient, request expedited review explicitly and attach the documentation that explains the urgency.

Diary the decision deadline

Seven calendar days for a standard Medicare Advantage decision, 72 hours for expedited, and seven calendar days for a standard fee-for-service request under the outpatient and DMEPOS programmes. Silence past those dates is something you can act on.

Track expiry and course-of-treatment scope

Record what was approved and for how long, and raise renewals before the last covered visit. Where a course of treatment is involved, hold the plan to the requirement that the approval lasts as long as the treatment remains necessary.

Appeal against the stated reason

Denials must now carry a specific reason. Read it, answer it directly, and treat the appeal as the default rather than the exception, because the published overturn rates do not support treating a denial as final.

Medtransic runs prior authorization for practices as part of the revenue cycle, across Original Medicare, Medicare Advantage and commercial plans. If authorizations are slipping, or denials go unappealed because nobody has the hours, a free revenue audit will show you what it is costing.