Shares of Humana fell 5 percent Wednesday after a Centers for Medicare and Medicaid Services report showed the health insurer's membership in certain highly rated Medicare plans declined.
Although the company raised its full-year guidance, and argued that the ratings don't reflect its current business, shares of the stock tumbled.
The Stars-quality ratings report for the 2018 plan year published on Wednesday said the insurance company's July 31 membership in 4-Star Medicare plans or higher declined to about 37 percent, or 1.17 million members. That's down from about 78 percent, or 2.15 million members, the prior year, according to CMS.
The Medicare Star Quality Ratings system is used to measure how well Medicare Advantage and prescription drug plans perform, and establish bonus payments.
Humana attributed the decline to the impact of lower scores for certain Star measures as a result of its recently closed program audit by CMS. The company also said the decline does not account for certain actions it plans to take to mitigate the negative impact of the published ratings on Star bonus revenues for 2018.
Humana said it intends to file for reconsideration of certain star ratings, saying they "do not accurately reflect the company's actual performance."
The company also said another measure, the Healthcare Effectiveness Data and Information Set, or HEDIS, is at a record high.
Humana said it doesn't expect this development to hurt its Medicare membership growth next year.
The insurer raised its 2016 earnings outlook to $9.50 a share on an adjusted basis from $9.25 a share, citing better-than-expected performance in Medicare Advantage business for the increase.
The company also boosted its third-quarter earnings forecast to about $3.15 a share, adjusted, from a prior estimate of $2.77 a share.
The report comes as Humana prepared for a December trial in the Department of Justice's attempt to challenge Humana's plans to merge with Aetna.
Humana's stock is down more than 5 percent year to date.