Health insurer Aetna Inc reported a slight rise in net income on Wednesday as membership increased, but it cited higher-than-projected medical costs in its commercial business that serves employers.

Net income rose to $437.8 million, or 95 cents per share, from $431.6 million, or 85 cents per share, a year earlier.

Excluding items, earnings of 96 cents were 3 cents ahead of the average forecast of analysts, according to Reuters Estimates.

Revenue rose 11 percent to $8.61 billion.

The company's commercial medical benefit ratio, which measures the amount of premiums spent on medical costs, worsened to 81.7 percent from 79.8 percent a year earlier. Aetna previously projected the ratio would be between 80.2 percent and 80.8 percent for the year.

People who are losing their jobs and taking COBRA post-employment insurance are using more medical services than expected, Aetna said. It also said people are using more services, such as getting more tests, when they visit the doctor.

The Hartford, Connecticut-based company also said it took more reserves to cover medical costs from prior quarters.

Aetna's health-plan membership stood at 19.1 million at the end of March, up about 9 percent over a year earlier.

The company said it continued to expect 2009 operating earnings of $3.85 to $3.95 per share.

(Reporting by Lewis Krauskopf; Editing by Lisa Von Ahn)