Aetna reported a 15 percent drop in earnings, but the results beat analysts' expectations as the insurer reported higher revenue driven partly by increased premiums and sales at newly acquired businesses.

Net income for the quarter was $457.6 million, or $1.32 per share, compared with $536.7 million, or $1.39 per share, during the same period a year before. Analysts polled by Thomson Reuters were expecting, on average, $1.25 per share.

The Hartford-based health insurer reported revenue of $8.8 billion for the second quarter, up from $8.3 billion during the same period in 2011. Growth in Medicare Advantage plans, the addition of Genworth's Medicare Supplement business and higher premiums for commercial, mostly employer-based, health insurance drove the growth in revenue. Aetna also benefited from added revenue related to 2011 acquisitions.

One key metric all health insurers are watching is medical loss ratio, the percentage of premium dollars spent on medical treatment for customers. The company spent a greater percentage of premiums on medical costs — 82.4 percent of premium dollars during the quarter compared with 79.7 percent during the same period last year.

Aetna's Medicaid business had the highest ratio at 90.1 percent, followed by 82.9 percent for Medicare and 81.7 percent for its commercial health insurance plans.

Goldman Sachs analysts Matthew Borsch and Sam Wass said in a research note that "overall, results and earnings quality look solid" even though the commercial medical loss ration at 81.7 percent is above Wall Street estimates.

The company's total health-insurance membership — excluding dental and pharmacy benefits — was 18 million as of June 30, which included 16.2 million in commercial, employer-based health insurance, 437,000 in Medicare Advantage plans, 1.2 million in managed Medicaid plans and 183,000 in Medicare supplement plans. Total medical membership was down from 18.2 million at the end of the second quarter in 2011, driven by a decline in commercial health insurance and managed Medicaid plans while enrollment grew in Medicare Advantage and Medicare Supplement.

Membership, however, was up from 17.9 million at the end of the first quarter.

"We continue to project membership growth for 2012, supported by a second-quarter increase of more than 100,000 members across our businesses," said Aetna chairman and CEO Mark T. Bertolini. "We have had some excellent recent mid-year success, with the expansion of our Missouri Medicaid relationship and winning the commercial account for the State of Maine. We are optimistic about our ability to sustain momentum into 2013, with wins such as the new group Medicare opportunity awarded by our long-standing customer Teacher Retirement System of Texas to convert existing commercial members into Medicare Advantage members."

Enrollment in dental insurance plans dropped from 13.79 million to 13.59 million between June 30, 2011, and the end of last month. Enrollment in the company's pharmacy benefits plans dropped from 8.78 million to 8.66 million during the same period.

"Based on our second quarter results, we are increasing our full-year 2012 operating earnings guidance to a range of $5.00 to $5.10 per share," said Aetna's chief financial officer Joseph M. Zubretsky.

Shares of Aetna's common stock were down 1.08 cents Tuesday, at $36.06.

Note: a previous version of this story cited revenue for the health care business only. Corrected version updated at 1:22 p.m.