CMS Moves to Align Quality Reporting With Medicare Assignment
Medicare’s accountable care rules have long treated patient ownership as a moving target, and physicians in the Medicare Shared Savings Program have lived with the consequences quarter after quarter. A roster can shed long-established patients while gaining others who have never truly entered the practice’s orbit, yet those same names can still appear on quality lists when a gap needs closing. The result is a system where attribution, quality reporting, and financial accountability do not always describe the same population.
CMS is now proposing two changes that would narrow part of that mismatch. Beginning in 2027, quality reporting would be limited to patients actually assigned to the accountable care organization. Beginning in 2028, the assignment rules themselves would change. Both steps move the program toward cleaner alignment, but neither proposal eliminates the underlying mechanism that drives turnover in the roster.
One quarter can bring a fresh batch of long-tethered patients onto the list and send others away. The administrative churn is not subtle.
A Quality Denominator That Finally Matches the Attributed Population
Under the current setup, one visit can place a patient into a physician’s Medicare clinical quality measure denominator even when that patient is not assigned to the ACO for savings. The quarterly list is built from Medicare fee-for-service claims, and a single qualifying claim can make an ACO responsible for screening, monitoring, and care-gap closure for a patient who may not belong to the organization from a shared-savings standpoint. That creates a blunt asymmetry: a physician can be measured on a patient after a short encounter, yet remain uninvolved in the spending benchmark that determines whether the ACO wins or loses financially.
The 2027 proposal would end that split by counting only assigned patients for Medicare clinical quality measures. In practical terms, the quality population and the attributed population would finally match. A patient who is not assigned would no longer generate quality accountability, and a one-off encounter would not saddle the ACO with a stranger’s overdue diabetes care, eye exam, or kidney health evaluation.
The policy change is small on paper and consequential in operation. Quality measures only make sense when the denominator reflects the real care relationship. Otherwise, the measure becomes a claim-history exercise instead of a test of longitudinal care.
Assignment Still Runs on Dollars, Not Continuity
The harder problem sits in the assignment formula itself. Shared-savings attribution remains tied to a plurality of primary care allowed charges, not to visit counts or years of care. The rule favors whichever billing pattern wins the dollar comparison during the assignment window. A patient seen for decades by one clinician can fall off the roster if another practice crosses the plurality threshold. Another patient can enter because the billing math says so, even if the therapeutic relationship has been thin.
CMS proposes two changes to expand the number of beneficiaries in accountable care relationships beginning in 2028. The first would stop counting certain outside-ACO charges when ACO clinicians bill for the same patient both inside the ACO and through a practice outside it. CMS estimates that this would add almost 98,000 assigned person-years, about 1%. The rationale is straightforward: current rules may let ACOs avoid accountability for some high-cost, at-risk patients when outside billing distorts the plurality calculation.
The second proposal would widen the front door to assignment. Under the current rule, a patient must have a clean record for the full assignment window, with no months of Part A-only, Part B-only, or Medicare Advantage enrollment. CMS would loosen that requirement so that one month of Part A and Part B without Medicare Advantage would be enough, regardless of what happened during the other months. CMS estimates that change would add about 248,000 assigned person-years, roughly 2.5%.
Those numbers matter because assignment is not a clerical detail. It determines who gets counted in the benchmark years, who appears in the performance year, and whose spending drives shared savings or losses. When the list moves, the math moves with it.
Why a Stable Roster Matters More Than a Bigger One
A stable patient list is not a cosmetic preference. It is the foundation of accountable care. Benchmark spending comes from the patients who would have been assigned during the benchmark years. Performance-year results come from the patients assigned now. Risk scores, per-capita spending, and quality denominators all depend on the same roster. If the roster shifts too much, the comparison loses meaning.
A long-standing patient who disappears from the list takes years of managed chronic disease with them. A newly assigned patient who was never really under the ACO’s day-to-day care brings spending history the organization did not shape. Both forms of churn weaken the connection between physician effort and program outcome. An ACO cannot reliably demonstrate control of cost or quality for patients it cannot consistently identify.
That mismatch also distorts the patient experience at the bedside. Physicians may be held responsible for care gaps discovered after a single visit, while other patients with years of continuity vanish from the roster when the program calculates savings. The result feels less like accountable care and more like shifting administrative weather.
CMS Acknowledges the Problem, But Only Partly
The proposal does address a real defect in the current structure. Starting in 2027, aligning quality reporting with actual assignment would remove one of the most glaring inconsistencies in MSSP administration. The 2028 assignment changes would also broaden participation, at least numerically. CMS wants every person in traditional Medicare in an accountable care relationship by 2030, with ACOs as the main vehicle for getting there.
Yet the changes leave the core plurality-by-dollars rule intact. That rule remains the engine of most roster churn. A system built on billing weight can be widened, but it is still being driven by a metric that can misrepresent continuity of care. As long as assignment depends on a dollar comparison, a decades-long primary care relationship can be outweighed by a smaller set of charges elsewhere.
For physicians, the practical question is not whether CMS has moved in the right direction. It has. The more relevant question is whether the roster will become steadier enough to make quality measurement and shared-savings accountability look like the same clinical relationship. The proposal improves the fit. It does not fully solve the mismatch.
The details still matter most where the patient list is built, because that list determines who is measured, who is assigned, and who counts when Medicare calculates savings. Until assignment becomes less vulnerable to billing noise, accountable care will remain only partially accountable.