Federal auditors found that medical records did not support the diagnosis codes UnitedHealthcare of Wisconsin submitted to Medicare in 183 of 250 sampled enrollee-years, and estimated the insurer was overpaid at least $46.9 million for 2020 and 2021. The HHS Office of Inspector General issued the audit of Medicare Advantage contract H5253 on September 10, 2026. OIG recommended that the company refund the estimated overpayments; United disputed some of the findings and asked the watchdog to withdraw all four recommendations.
Why diagnosis codes drive Medicare Advantage payments
CMS pays Medicare Advantage plans a monthly amount for each enrollee, adjusted for age, gender and health status. The sicker a member appears on paper, the higher the payment. Plans collect diagnosis codes from doctors and hospitals and forward them to CMS, which uses a given year’s diagnoses to set payments for the following year. In 2024, CMS paid Medicare Advantage organizations $494 billion, or 44 percent of all Medicare payments, according to the OIG audit.
If a code is not backed by the medical chart, the member’s risk score is overstated and Medicare overpays. OIG has been auditing plans one contract at a time, focusing on diagnoses its data mining identified as especially prone to error. This review covered 11 such groups, including acute stroke, heart attack, embolism, five types of cancer, sepsis, severe pressure ulcers and potentially mis-keyed codes.
UnitedHealthcare of Wisconsin, based in Minneapolis, covered 676,374 enrollees under contract H5253 as of December 2021. CMS paid the contract approximately $16.6 billion for the 2020 and 2021 payment years.
Keeping plan paperwork straight. A coding audit is a reminder that what a plan reports and what a member actually pays are two different ledgers, and the medication and cost tracker in The Medicare Cost & Coverage Protection Kit keeps the second one in view.
Where the errors showed up
The error rates were highest in diagnoses that describe an acute event or an active cancer. United’s submissions were unsupported in all 20 sampled enrollee-years for breast cancer and all 20 for colon cancer, 19 of 20 for acute stroke, 19 of 20 for heart attack, 19 of 20 for ovarian cancer and 18 of 20 for prostate cancer. The rates were lower for sepsis (6 of 20) and pressure ulcers (9 of 20).
A recurring pattern involved past illness coded as current illness. In many stroke and cancer cases, the charts showed that a patient had previously had the condition, but not that it was active at the time of the visit. OIG noted that a “history of” diagnosis, which typically should have been used, does not raise a plan’s payment. Across the sample, the unsupported codes produced $722,280 in overpayments, which OIG projected to at least $46,913,121 for the two-year audit period.
OIG found United had compliance measures in place, including provider outreach, annual coding reviews, 156 hours of training for new coders and a 95 percent accuracy requirement. United also had a filter to block acute stroke codes, but it applied only to in-home health visits and chart reviews, not to claims submitted directly by providers. Given the error rate, OIG concluded the company’s procedures could be improved.
United’s objections and what happens next
OIG made four recommendations: refund the $46.9 million; review 81 enrollee-years in the potentially mis-keyed group that auditors did not examine; identify similar errors after the audit period and refund any overpayments; and strengthen its compliance procedures.
United called the audit and extrapolation methods “fundamentally flawed” and challenged findings for 33 enrollee-years. After a second look, OIG’s independent medical reviewer reversed eight of those decisions and upheld 25, which cut the error count in the final report from 191 to 183. The company also argued that CMS had already recouped the 2020 portion through a $241 million medical loss ratio rebate. OIG said that rebate mechanism falls outside the audit and does not change a plan’s obligation to return overpayments.
United raised several broader objections as well. It argued that OIG could not find overpayments without applying a fee-for-service adjuster, that the audit ignored underpayments from codes plans failed to submit, that a 250-case sample was too small for reliable extrapolation, and that it was not obligated to review additional mis-keyed diagnoses or audit years after 2021. OIG maintained its recommendations.
OIG recommendations are not final determinations. CMS decides whether an overpayment exists and how to recover it, and a plan can appeal through the risk adjustment data validation appeals process. The $46.9 million figure is a recommended recovery, not money already returned to Medicare.
What this means for Medicare beneficiaries
The audit targets the plan’s billing to the government, not its members. No enrollee owes money, faces a coverage change or needs to file anything because of it. Still, the findings touch older Americans in two practical ways.
First, the cost of overpayments is spread across the program. Medicare Advantage payments come from the same trust funds that pay for traditional Medicare, and the standard Part B premium is set to cover about a quarter of Part B spending, including the Part B share of payments to private plans. Coding that inflates plan revenue therefore adds pressure on costs every beneficiary shares.
Second, the diagnoses at issue sit in patients’ own medical charts. A stroke or cancer coded as current when it is in the past can follow a patient from visit to visit. Under federal HIPAA rules, patients have the right to obtain copies of their medical records and to ask a provider to amend information they believe is wrong. Reviewing visit summaries after annual wellness visits and in-home health assessments is a simple way to spot a condition listed as active when it is not.
For members of UnitedHealthcare plans, benefits continue unchanged. Those reconsidering their coverage for 2027 can compare options on Medicare’s Plan Compare during Open Enrollment, which runs from October 15 through December 7.
A plan’s billing problems do not show up on a member’s pharmacy receipt
OIG’s findings concern what United told Medicare, while the costs that land on a household come through premiums, copays, drug prices and coverage decisions that each need their own tracking.
The Medicare Cost & Coverage Protection Kit includes a medication and cost tracker, the new Part D out-of-pocket cap, the prior-authorization appeal steps and 51 state Medicare cost-help packs for checking whether a household qualifies for help with those bills.
Track what the plan actually charges with The Medicare Cost & Coverage Protection Kit.
This article was prepared with AI assistance and reviewed against the linked official sources.
