Shares of Minnetonka-based UnitedHealth Group Inc. closed at a record high Wednesday after a better-than-expected earnings report and an upbeat commentary for growth in 2015.

The nation's largest health insurer reported promising enrollment trends during the fourth quarter, particularly in government programs, and only moderate growth in medical costs.

Plus, analysts were impressed by earnings growth at the company's Optum health services division, which includes management of pharmacy benefits and information technology for reducing costs and improving quality.

"It was hard to really find anything wrong in there," said David Heupel with Thrivent Financial in Minneapolis. "It looked good."

Early last year, UnitedHealth officials were cautious about the business impact from the federal Affordable Care Act, the sweeping health law that brought new taxes on insurers and downward pressure on Medicare payment rates to health plans. In the end, the health law cut about $1 billion, or $1 per share, from UnitedHealth earnings during 2014, officials said Wednesday.

But growth prospects related to the health law are coming more clearly into focus for UnitedHealth, which employs about 14,000 people in Minnesota.

Stephen J. Hemsley, chief executive of UnitedHealth says its footprint in Medicaid continues to grow.

The Affordable Care Act gave states the option to significantly expand Medicaid health insurance programs for low-income residents. Many states hire UnitedHealth to manage Medicaid benefits, so the expansion of coverage through the program helped drive a 29 percent increase in Medicaid revenue during 2014 compared with the previous year.

"Our footprint in the Medicaid market continues to grow, now reaching states where nearly 60 percent of the Medicaid community reside," said Stephen Hemsley, the UnitedHealth chief executive, during a conference call with investors. He added later: "We expect to continue this pattern of broad-based growth in 2015, with revenues expected to grow 15 to 17 percent this year."

The insurer is making a bigger play on health insurance exchanges this year by selling products on government-run marketplaces for 23 states. So far, the company has seen more than 400,000 sign-ups on these exchanges, Hemsley said. Jeff Alter, chief executive of the company's UnitedHealthcare insurance division, said the tally could hit about a half-million enrollees by the time open enrollment closes on Feb. 15.

UnitedHealth expects to sell products on even more state exchanges in 2016. But the company's plan to sell products in all parts of California through that state's exchange were blocked by state regulators, who cleared UnitedHealth to sell in just a small handful of markets.

The rate of increase in medical costs during the fourth quarter remained relatively low, company officials said, and stood at a little less than 5.5 percent for 2014. The company expects costs to grow by about 6 percent this year.

"With December behind us and the majority of January behind as well, we are not seeing any indication or evidence of an increase in utilization," said Dan Schumacher, chief financial officer at UnitedHealthcare.

UnitedHealth expects cost increases in 2015 due to new treatments for hepatitis C, but did not specify Wednesday by exactly how much, said Peter Costa, an analyst with Wells Fargo Securities.

In a note to investors, Costa wrote: "Costs for 2014 were about in line with [UnitedHealth's] revised outlook following higher-than-expected costs of $100 million across all of the company's segments" during the first quarter of 2014. Competitive medication treatments have since been launched, so UnitedHealth said "it was in negotiations with manufacturers," Costa wrote.

For the quarter that ended Dec. 31, UnitedHealth reported net earnings of $1.51 billion, an increase of about 6 percent compared with the same period last year. Earnings per share came in at $1.55, 5 cents per share better than expected by analysts surveyed by Thomson Reuters.

Fourth-quarter revenue of $33.43 billion was about 7 percent greater than last year.

For 2014, UnitedHealth Group posted net earnings of $5.6 billion, or $5.70 per share, on $130.5 billion in revenue. The insurer is Minnesota's only publicly traded company with more than $100 billion in annual revenue.

For 2015, the company expects revenue in a range of $140.5 billion to $141.5 billion, and earnings per share in a range of $6 to $6.25.

Shares closed Wednesday at $109.32, up $3.70, or 3.5 percent on the day.

Christopher Snowbeck • 612-673-4744

Twitter: @chrissnowbeck