UnitedHealth Group Inc (NYSE:UNH) stock is eyeing its worst single-day percentage loss since April, last seen down 19.8% to trade at $281.96. The company posted mixed fourth-quarter earnings results, with profits of$2.11 beating estimates by one cent, while revenue of $113.2 billion came in below expectations. The Centers for Medicare & Medicaid Services proposal to raise Medicare Advantage rates by 0.09% -- far below expectations of a 4-6% increase -- is weighing on the shares, as well as UnitedHealth's s ...