Switching Medicare Advantage plans mid-treatment used to carry a real risk that a new insurer would simply restart the approval process, forcing a patient already in chemotherapy, physical therapy, or another extended course of care to wait on a fresh prior authorization decision. A federal rule closed much of that gap: a coordinated care plan cannot demand new prior authorization for an active course of treatment already underway when a member switches into it, and it must honor that treatment for a guaranteed minimum transition period.
The 90-day rule and what triggers it
The protection comes from CMS’s 2024 Medicare Advantage and Part D final rule, which “requires coordinated care plans to provide a minimum 90-day transition period when an enrollee currently undergoing treatment switches to a new MA plan, during which the new MA plan may not require prior authorization for the active course of treatment.” The trigger is simply an active course of treatment in progress at the moment of the switch, not a specific diagnosis list, which means the rule can cover anything from a multi-week physical therapy regimen to an ongoing infusion schedule, provided the treatment was already underway before the new plan took over.
The rule reaches further than plan-to-plan moves. CMS’s fact sheet specifies this transition protection applies whether a member is switching from a previous Medicare Advantage plan, or from Original Medicare fee-for-service, into a new Medicare Advantage plan, and it also covers someone newly enrolling in Medicare who joins a Medicare Advantage plan while already receiving ongoing care. That breadth means the protection is not limited to people actively shopping plans during Annual Enrollment; it follows anyone whose care continuity would otherwise be disrupted by any transition into a new coordinated care plan.
The transition-period requirement did not emerge in isolation. CMS’s fact sheet ties the broader package of prior-authorization changes to concerns raised in a federal Office of Inspector General review, and the final rule responds by requiring Medicare Advantage plans to follow the same national and local coverage determinations already used in Original Medicare, rather than inventing stricter internal standards. The 90-day transition rule sits inside that same push: a plan cannot use a change in insurer as a backdoor way to apply a tougher standard than Original Medicare itself would apply to the identical ongoing treatment.
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What “must keep paying” does not mean
The rule guarantees a transition window, not permanent coverage of every element of a treatment plan on the new insurer’s terms indefinitely. CMS’s fact sheet is specific that the requirement is a minimum 90-day period during which prior authorization cannot be newly imposed on the treatment already in progress; it is not framed as an open-ended bar on the new plan ever reviewing that care going forward. The same final rule separately requires that once a prior authorization approval is granted for a course of treatment, it “must be valid for as long as medically reasonable and necessary to avoid disruptions in care,” a standard tied to the patient’s medical history and the treating provider’s recommendation rather than to a fixed calendar length.
The rule also tightens what coordinated care plans can use prior authorization for in the first place, limiting it to confirming a diagnosis or medical criteria and to ensuring medical necessity, rather than as a general cost-control gate. CMS additionally required every Medicare Advantage organization to stand up a Utilization Management Committee that reviews its own prior authorization policies annually against Original Medicare’s coverage rules, a structural check meant to keep individual plans from drifting toward stricter standards than Traditional Medicare applies to the same care.
None of this removes a patient’s right to challenge a denial if one happens anyway. If a new plan does deny or interrupt a covered treatment despite these protections, Medicare’s claims, appeals, and complaints process remains the enforcement backstop, letting a member formally dispute a coverage or payment decision rather than simply absorbing an incorrect denial.
A denial that violates the 90-day transition period is not a gray area open to interpretation; it is a plan failing to follow its own binding obligation under the final rule, which strengthens a member’s position if they do escalate to a formal appeal. That distinction matters practically, because an appeal grounded in a plan ignoring a specific regulatory duty tends to move faster and more decisively than one contesting a purely subjective medical-necessity judgment call.
Why the notification duty matters as much as the coverage duty
A second piece of the same final rule works alongside the transition period: Medicare Advantage organizations must now notify enrollees when their behavioral health or primary care provider is dropped from the network mid-year, closing a gap where patients previously learned about a network change only when a claim was rejected. Paired with the 90-day transition protection, the combined effect is that a patient mid-treatment is now supposed to be told about a disruptive change and shielded from an immediate authorization fight over care already in motion, rather than facing both problems silently at once.
The practical value of the rule shows up most clearly for patients with long, sequential treatment plans, where a gap of even a few weeks can undo clinical progress. A 90-day floor does not guarantee coverage forever, but it converts what used to be an open question, resolved plan by plan and sometimes only after an appeal, into a defined right that a patient or their provider can point to the moment a new insurer questions treatment that had already been approved somewhere else. If that right is not honored, Medicare’s formal appeals process exists specifically to correct it.
This article was researched and drafted with the assistance of artificial intelligence.
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