Payer-Specific Denial Patterns by Major Insurer

Every payer denies claims for its own reasons, but the machinery behind those denials draws from the same three levers. The first is prior authorization: requiring sign-off before a service that didn't need it last year, or narrowing the clinical criteria for something that already required approval. The second is algorithmic adjudication, automated review tools that apply rule sets to claims at a volume and speed no human reviewer could match. The third is policy change velocity: insurers update coverage rules, coding requirements, and clinical guidelines on their own schedule, often without giving providers meaningful notice before the new rule starts costing them money.

Here's the asymmetry that turns this into a structural problem rather than a one-off headache. Payers track every denial they issue, by code, by reason, by provider. Most practices don't track denials by payer at all until a pattern has already burned through months of revenue, and by the time someone notices the trend on a spreadsheet, the money is already gone.

Private payers, commercial and marketplace plans alike, deny claims at rates well above public payers like Medicare, according to KFF research. That gap is exactly where payer-specific intelligence pays off: the highest-risk claims in most practices sit concentrated in a handful of commercial and marketplace relationships, not spread evenly across the whole mix.

Then there's the appeal paradox, and it's the part that should bother practices most. A large majority of appealed denials get overturned. Yet the overwhelming majority of denied claims are never appealed at all. Payers benefit, structurally, from practices doing nothing, and doing nothing is the default outcome absent a deliberate process built to prevent it.

What follows is a payer-by-payer map: which claim types each insurer targets, which procedural triggers it leans on, and what its appeal posture actually looks like once a denial lands.

UnitedHealthcare: the highest-volume payer with the most aggressive algorithmic adjudication

UnitedHealthcare's prior authorization denial rate in Medicare Advantage sits among the highest of any major insurer, meaningfully above a competitor like Humana. That gap alone should change how a practice with a heavy MA panel handles documentation, before a claim ever goes out the door.

The nH Predict story is the clearest illustration of automated review going wrong at scale. A 2023 lawsuit alleged that UnitedHealthcare used an algorithm called nH Predict to deny post-acute care claims that treating physicians had already approved, and the plaintiffs cited an error rate high enough to suggest the tool was overriding clinical judgment rather than supporting it. A U.S. Senate Permanent Subcommittee on Investigations report found that UnitedHealthcare's post-acute denial rate more than doubled after it started using naviHealth and nH Predict. The court let the case move forward, and as of March 2026, ordered wide-ranging discovery into how the tool was actually implemented. This is not a settled risk; it's an evolving one for any practice billing post-acute services. Optum, for its part, says nH Predict is a care-support tool shared with providers and caregivers, and that medical necessity decisions come from physicians following CMS guidance, not from the algorithm itself. Read that defense skeptically: a doubling of the denial rate right after a tool's rollout raises real questions about how much clinical judgment actually shaped those decisions.

UnitedHealthcare also shows up in a June 2026 OIG report as one of the insurers denying a high share of requests to move patients into long-term care hospitals or rehab facilities after a hospital stay. That's a distinct risk window from prior auth denials. It hits after the patient is already admitted and needs a change in care level, which means the documentation fight starts over from scratch.

Then there's the appeal clock. UnitedHealthcare's commercial appeal window runs shorter than half of what Aetna, BCBS, and Cigna each allow. A practice running every payer off one shared appeal calendar is the most exposed here, because a missed UnitedHealthcare deadline forfeits the appeal outright, regardless of whether the denial had any clinical merit at all. Tracking UnitedHealthcare on its own deadline calendar isn't a nice-to-have; it's the floor for protecting that revenue.

UnitedHealthcare has also announced it will drop prior auth for a meaningful share of procedure codes and roll out a gold-card program for qualifying providers. Practices should check which codes are actually affected in their own contracts rather than assume the announcement has taken effect everywhere at once, because rollout timing and contract terms rarely move in lockstep with a press release. The highest-risk categories with this payer remain post-acute and long-term care transitions, behavioral health parity claims, and anything requiring prior auth under a Medicare Advantage plan.

Aetna and CVS Health: elevated MA denial rates and a Medicaid prior auth problem worth knowing

Aetna's Medicare Advantage prior auth denial rate sits in the same high range as UnitedHealthcare's, well above Humana's, which makes it a real exposure for any practice with a substantial MA population.

Contract-level variation is where this gets operationally tricky. Aetna's MA filings show sharply different denial rates depending on the specific contract number covering a given plan: one contract shows approvals close to universal, another shows meaningful denial volume. Two patients, both on "Aetna Medicare Advantage," can carry very different denial risk depending on which contract sits behind the card, and that's a detail most billing systems never surface on their own.

The appeal overturn rate for Aetna MA denials runs high, with more than half reversed on appeal. That's a strong signal that a large share of Aetna denials are worth fighting rather than writing off as a cost of doing business.

CVS Health, Aetna's parent, was named alongside UnitedHealthcare and Humana in that June 2026 OIG report for high rates of post-hospital care transition denials in Medicare Advantage. Aetna's commercial book and its MA book should be treated as separate payer relationships with separate policy sets, not one billing relationship wearing two names. High-risk categories: post-acute transitions, step therapy documentation, and durable medical equipment under MA plans.

Humana: the post-acute denial outlier and a separate AI litigation thread

Humana's Medicare Advantage prior auth denial rate runs substantially lower than UnitedHealthcare's or Aetna's, making it the more permissive of the three at the initial authorization stage.

That lower number is misleading if a practice reads it as blanket safety, and plenty do. Humana still shows up in the June 2026 OIG report as one of the insurers denying post-hospital care transitions at high rates, which means the risk shifts rather than disappears once a patient is already admitted and needs a level-of-care change. A separate class action against Humana over its use of an algorithmic review tool survived a motion to dismiss in August 2025. The tool and its scope differ from UnitedHealthcare's nH Predict, but the underlying allegation is the same: automated denials overriding what the treating physician actually decided.

Practices billing Humana MA for skilled nursing, rehab, or long-term care transitions should treat those as high-alert categories requiring documentation built before the fact, not scrambled together after a denial lands. A lower PA denial rate says nothing about post-admission risk. Those are two different moments in the claim's life, governed by different rules, and conflating them is exactly how a practice gets caught flat-footed.

Humana's appeal behavior deserves its own tracking, too. The broader OIG finding that MA appeal win rates run very high overall suggests Humana denials are contestable. But low appeal volume industrywide means most practices are simply leaving that money on the table instead of fighting for it, and Humana is no exception to that pattern.

Cigna: an algorithmic speed controversy and a high Medicaid marketplace denial rate

ProPublica reporting and the litigation that followed allege Cigna used a review tool called PXDX that let reviewers clear denials at a pace of roughly one per second, a speed that makes individual clinical review functionally impossible at that volume. Cigna disputes the characterization of the tool as an AI system and says it's been mischaracterized in reporting; a judge allowed the case to proceed in March 2025.

The operational read for practices is blunt: if Cigna denials come out of a machine running at one per second with no meaningful individual review behind them, treating the initial denial as a considered medical judgment carries real risk. Appeal with strong clinical documentation and expect a better outcome than the first decision suggests.

Cigna's Medicaid prior authorization denial rate ranks among the higher figures reported for major insurers in available data, and its appeal overturn rate runs notably lower than a payer like Aetna's. High denials paired with low overturn odds is close to the worst profile a practice can face: more denials arrive, and fewer of them come back once appealed. Cigna claims need the investment made upfront, not after the fact, meaning correct coding, complete documentation, and verified prior auth before submission, because the downstream appeal path is less reliable than it is with other payers. High-risk categories: behavioral health, specialty drugs requiring step therapy, and any service line where Cigna has recently added clinical criteria.

Anthem/BCBS plans: the federation problem that standard payer intelligence misses

Anthem's overall marketplace denial rate lands in the middle of the pack among major insurers. That single number conceals more than it reveals.

Blue Cross Blue Shield isn't one payer. It's a federation of independent licensees, each running its own coverage policies, its own prior auth lists, and its own clinical criteria. A practice billing BCBS across state lines is, in effect, billing several different payers that happen to share a brand and a card design. A policy update from one BCBS licensee doesn't automatically apply to another, which leaves practices treating out-of-state patients on a different BCBS entity exposed to rules they never saw coming.

Blue Cross Complete, the Michigan Medicaid plan under the BCBS umbrella, makes the point sharply: its Medicaid prior auth denial rate ranks among the highest of any major insurer for any plan type in available data, a figure that would vanish entirely inside a national Anthem average. Treating "Anthem" as a single payer obscures exactly the risk that matters most here. On the appeal side, Anthem and most BCBS plans allow a longer appeal window than UnitedHealthcare, giving practices more runway to recover denied revenue, but only if denials get tracked by the specific BCBS entity rather than lumped into one generic "BCBS" bucket. Practices should build policy tracking for each BCBS licensee they actually bill, not rely on national BCBS guidance that may not apply to the plan in front of them.

Oscar Health and Molina: the high-denial marketplace challengers practices often underestimate

CMS Transparency in Coverage data for plan year 2024 puts Oscar and Molina at the top of the denial-rate list among major marketplace insurers, meaningfully above UnitedHealthcare, Aetna, or Cigna in that same marketplace context.

Oscar markets itself as the simpler, more transparent insurer, built on newer technology and a cleaner member experience. Its actual ACA marketplace denial rate, though, is the highest among major marketplace insurers in the data, and that gap between brand and behavior deserves more scrutiny than it gets. A tech-forward payer isn't automatically a lenient one; the data here suggests the relationship can run the other way entirely. Oscar concentrates heavily in ACA marketplace plans, so practices in markets with high ACA enrollment shouldn't assume Oscar claims move any easier than a legacy payer's.

Molina concentrates heavily in Medicaid and marketplace plans, often in lower-income markets, which means its high denial rate lands on a patient population with less capacity to navigate an appeal or absorb an out-of-pocket bill if the coverage decision doesn't get reversed. Practices with Medicaid-heavy or dual-eligible panels need Molina-specific prior auth protocols built into intake, not a generic Medicaid workflow stretched thin to cover a payer with its own rules.

Neither Oscar nor Molina has drawn the same volume of public reporting on denial triggers that UnitedHealthcare or Cigna has. Practices should treat any sudden cluster of denials from either payer as a signal to pull claims by denial reason code immediately, rather than wait months for the pattern to become obvious on its own.

Ambetter and regional marketplace plans: the high-denial tail that flies under the radar

Ambetter, operated by Centene, posts a marketplace denial rate in Texas that ranks among the highest reported for any major marketplace insurer in available data. Regional carriers like Ambetter often operate in markets with limited provider network competition, which removes much of the pressure to keep denial rates low in order to retain physicians in the network.

The pattern here echoes Cigna: a high denial rate paired with a low appeal overturn rate. That combination calls for prevention before submission as the primary defense, with appeals serving as a weaker backstop, because the appeal path simply isn't as reliable. Practices in states with heavy Centene or Ambetter marketplace penetration, Texas prominent among them, should treat these plans as primary payer relationships with their own scrubbing rules built in, not secondary afterthoughts trailing the commercial book. Regional plan policy updates rarely surface through the industry channels most practices already monitor, which makes direct contract review and denial-reason-code analysis the most dependable source of intelligence on these plans.

The prior authorization reform wave and what it actually changes for practices right now

CMS-0057-F, finalized in January 2024, requires affected payers to issue prior auth decisions within 72 hours for urgent requests and seven calendar days for standard ones, with key provisions taking effect in 2026. That's a real change to the clock.

The outcome is a separate question, and practices banking on faster decisions translating into more approvals are setting themselves up for disappointment. A payer can deny at exactly the same rate it always has, just faster, and the practice is no better off financially even though the answer arrives sooner. The rule also only reaches certain federally regulated payers. Commercial fully-insured plans and self-funded employer plans run on different timelines and carry different exposure, so a practice can't assume the rule protects every payer relationship on its books. CMS's own ten-year savings projection reflects administrative efficiency, meaning less staff time spent waiting on a decision, rather than an expectation that denial rates themselves will fall.

State-level reform is stacking on top of the federal rule, with a growing number of state bills taking aim at prior auth timelines and criteria on their own. None of this removes the need for payer-specific tracking. It raises the stakes for it: a faster denial still needs a faster, correctly-timed appeal, and the practices that already track deadlines by payer are the ones positioned to actually benefit when the clock speeds up.