Humana is among the largest providers of Medicare Advantage plans, which are privately run versions of the government's Medicare program that provides health coverage for the elderly. Enrollment in its lucrative Medicare Advantage business reached 1.76 million as of last Dec. 31, up 17 percent from a year ago. By January, enrollment had risen to about 1.89 million.

The company is coming off a subpar fourth quarter, when earnings fell 57 percent due to expenses partly associated with its Medicare offerings and an expansion into health care delivery. Humana incurred expenses from a change in the Medicare Advantage enrollment period, for the launch of a prescription drug plan teaming Humana and Wal-Mart and for charitable contributions. The company also absorbed costs associated with its acquisition of Concentra, which delivers occupational medicine, urgent care, physical therapy and wellness services.

Citi Investment Research analyst Carl McDonald tempered Humana's upbeat forecast for the quarter and full year in a longer-term assessment. "We're not more excited about the better financial outlook, mainly because Humana is still going to assume a 5 percent Medicare margin when it submits 2012 bids in June, so earnings guidance for 2012 will not be nearly as optimistic as results this year," he wrote in a recent note.

McDonald said that more moderate cost trends are among the possible upsides for Humana's operations this year.

Humana also offers Medicaid and commercial coverage and insurance for military members and their families.

WHY IT MATTERS: Humana is one of the nation's largest publicly traded health insurers, with about 10 million medical members and 7 million specialty members.

WHAT'S EXPECTED: Analysts expect Humana to earn $1.49 per share on revenue of $9.11 billion for the first quarter, according to FactSet.

LAST YEAR'S QUARTER: Humana said its first-quarter net income jumped 26 percent last year, due partly to its expanding Medicare Advantage business. The health insurer earned $258.8 million, or $1.52 per share, for the three months a year ago. Revenue grew nearly 10 percent to $8.44 billion.