Half a million more seniors were prescribed high-risk medications than reported by Medicare Advantage health plans, according to a new study.

Medicare Advantage health plans failed to report 500,000 prescriptions of high-risk medications to seniors.

This discrepancy, outlined in a report published Sept. 30 in the Annals of Internal Medicine, not only highlights the potential dangers of risky prescribing, but also calls into question the accuracy of measures used by the government to rate health plans for people older than 65.

The government considers a group of about 100 medications to be risky for senior citizens. To determine whether the reported number of high-risk prescriptions was correct, researchers from Brown University compared information provided by 172 Medicare Advantage insurers with prescription drug claims obtained from the same plans.

The researchers used information provided by the insurers to the U.S. Healthcare Effectiveness Data and Information Set (HEDIS), which includes data from more than 90 percent of the health plans in the country. This database helps health policy professionals and consumers see which plans are providing the best quality care.

Understanding the Basics of Medicare

Based on the information in HEDIS, the researchers found that the average rate of high-risk prescriptions reported by the health plans was 21.1 percent. When they looked at the actual drug claims for those same plans, however, the rate was 26.9 percent, meaning that the insurers had been under-reporting by 5.8 percent.

About 95 percent of the insurers erred in their own favor. Only nine out of the 172 plans came within one percent of the rate calculated by the researchers.

Using the calculated rate, the researchers also noticed that the Medicare Advantage plans have similar risky prescribing rates to Medicare fee-for-service plans. Previously, the Medicare Advantage plans looked like they were performing much better on this particular metric.

Because this type of measure is used to determine the quality of care provided by a given plan, the difference is likely to affect how plans are rated compared to one other.

“The plans that were the most accurate were the ones that suffered the greatest penalties when using the plan-reported rates,” says study author Amal N. Trivedi, MD, MPH, in a press release.

Plans that were off by more than 10 percentage points moved up an average of 49 places on the ranked list when using reported rates. The nine most-accurate plans, however, moved 43 spots down the list.

The researchers chose high-risk prescriptions because the data is easily available from a few public sources and the risk of these 100 or so medications for people over 65 is well-known.

This doesn’t bode well for other factors used by the government to rate Medicare Advantage health plans.

“There is reason to believe that if there is inaccuracy in this relatively straightforward measure, there could be inaccuracy in other, more complicated measures as well,” says lead author Alicia Cooper, MPH, Ph.D.

One thing the new study doesn’t address is whether the errors were intentional or part of a general problem with tracking and reporting data. The authors, though, called for greater government oversight of what is reported by health insurers.

“Policymakers should consider routine audits of publicly reported quality measures, including the HEDIS indicator of high-risk prescribing, to ensure the validity and reliability for patients and other stakeholders,” the study authors wrote.

Previous research has shown that many seniors are already taking risky drugs. In a 2013 paper in the Journal of General Internal Medicine, researchers found that 21 percent of Medicare Advantage enrollees were taking at least one high-risk medication, which comes out to 1.3 million people.

In addition, seniors in the southeastern U.S., women, and those living in poor areas were all more likely to receive prescriptions for risky drugs.

While the government’s rating of health plan quality is useful, seniors also need to take ownership of their own drug therapy.

Smart Ways Medicare Recipients Can Save on Prescriptions

The American Geriatrics Society Foundation for Health in Aging provides a regularly-updated list of drugs that may be inappropriate for people 65 years or older.

Seniors concerned about their prescriptions should talk to their doctor and pharmacist to see if any of their current medication can be stopped or replaced with a less-risky alternative.