Aetna vs. UnitedHealthcare: Which Insurer Denies More Claims?

Aetna and UnitedHealthcare are two of the largest health insurers in the United States, together covering tens of millions of Americans. But size doesn't mean fairness — and when your claim gets denied, you need to know what you're up against. Comparing their denial patterns, Prior Authorization Denied: How to Appeal" class="auto-link">prior authorization rates, and appeal outcomes reveals important differences that can affect your strategy.

Denial Rates by Insurer (2026)" class="auto-link">Denial Rates: The Raw Numbers

Federal data from the ACA marketplace consistently shows both Aetna and UnitedHealthcare among the higher-volume deniers nationally. UnitedHealthcare has drawn particularly intense scrutiny in recent years: a 2023 congressional investigation revealed that one of its Medicare Advantage subsidiaries denied 90% of prior authorization requests for skilled nursing facility care — a rate far above industry peers.

Aetna, meanwhile, has faced legal challenges and state regulatory actions related to algorithmic denial practices. A 2023 Reuters investigation found that Aetna used an AI-driven review tool that made coverage decisions in just seconds, without individualized medical review. A subsequent class-action lawsuit alleged this led to systematic underpayment and denial of legitimate claims.

For employer-sponsored plans, the picture is similar. Both insurers rely heavily on third-party utilization management firms, which conduct prior authorization reviews and often deny care that treating physicians consider medically necessary.

Prior Authorization: Where the Denials Begin

Prior authorization is the front line of insurer cost control — and both Aetna and UnitedHealthcare use it aggressively.

UnitedHealthcare requires prior authorization for a long list of outpatient procedures, imaging, and specialist visits. Physicians and hospitals have repeatedly reported that UHC's authorization portal frequently generates automatic denials that must then be appealed by clinical staff, consuming significant administrative time.

Aetna has similarly expanded its prior authorization requirements. In several states, Aetna has been cited by insurance commissioners for authorization delays that exceed legal timeframes, particularly for behavioral health services and specialty drugs.

The key difference: UnitedHealthcare tends to deny more frequently at the initial stage, but Aetna's denials are sometimes harder to overturn because they lean more heavily on proprietary clinical criteria that aren't always disclosed to enrollees.

Claim Denial Reasons: Common Patterns

Both insurers rely on a standard set of denial reasons, but the frequency differs:

• Medical necessity denials: UnitedHealthcare uses InterQual criteria; Aetna uses its own clinical policy bulletins. Patients denied for medical necessity by either insurer have the right to request the specific criteria used.
• Out-of-network denials: Both insurers have narrow networks, but Aetna's network gaps in rural areas have led to a higher rate of out-of-network denials for enrollees who had no in-network alternative.
• Experimental or investigational denials: Both insurers have denied coverage for newer treatments using this category, but Aetna has faced particular criticism for denying FDA-approved therapies as "experimental."
• Timely filing denials: UnitedHealthcare's complex claims submission systems have led to more timely filing denials compared to Aetna, particularly for smaller providers.

Appeal Success Rates

Here's the data that matters most: how often do denials get overturned on appeal?

State-level external appeal data (available in states like New York and California) shows that both insurers lose a meaningful percentage of external appeals — generally 30–50% of cases are overturned when patients push back through independent review. Internal appeal rates show lower overturn numbers but are still worth pursuing.

Patients appealing UnitedHealthcare denials tend to benefit from referencing InterQual criteria directly in their appeal letters, since UHC's decisions are theoretically bound by those guidelines. Aetna appeals are often more successful when you can demonstrate that Aetna's own clinical policy bulletin doesn't actually exclude your specific treatment.

Which Insurer Is More Difficult to Deal With?

Consumer complaint data from the National Association of Insurance Commissioners (NAIC) consistently places UnitedHealthcare among the highest complaint ratios among large national insurers. Aetna scores somewhat better on complaint ratios but has faced more class-action litigation over systematic denial practices.

In practical terms:

• UnitedHealthcare tends to deny faster and in higher volume, but appeals grounded in InterQual criteria can be effective.
• Aetna tends to deny on more nuanced medical grounds, requiring more detailed clinical documentation in appeals.

Both insurers are subject to the ACA's internal and external appeal processes, and both are required to provide a full and fair review of denials. If you're denied by either insurer, you have rights — and you can exercise them.

Fight Back With ClaimBack

Whether your claim was denied by Aetna, UnitedHealthcare, or any other insurer, ClaimBack helps you build a compelling appeal with the evidence and language that actually works. Start your appeal at https://claimback.app/appeal.

Related Reading

• How to Write an Insurance Appeal Letter
• What Is Medical Necessity?
• Internal vs. External Insurance Appeals