LOS ANGELES (MarketWatch) — Aetna Inc. shares surged in Friday trading after the health insurer offered a fiscal 2011 outlook that's ahead of Wall Street estimates.

The 2011 outlook of $3.70 to $3.80 a share compared with the $3.27 consensus estimate of analysts polled by FactSet Research.

That sent the shares higher by nearly 14% shortly after the opening bell. The stock ended trading Friday up 12.5% to $37.42. Aetna was the second-biggest gainer on the S&P 500.

Aetna AET made the prediction as it reported fourth-quarter results in which revenue was down but profit was up.

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The company earned $215.6 million, or 53 cents a share, compared with $165.9 million, or 38 cents, in the year-earlier period. Sales were $8.54 billion versus $8.76 billion.

Adjusted earnings for the latest quarter were 63 cents a share. Analysts polled by FactSet Research had expected the company to earn 62 cents.

Goldman Sachs analyst Matthew Borsch said in a note to clients Friday that not only was Aetna’s outlook well above forecasts, but its medical-loss ratio — reflecting the percentage of revenue devoted to patient treatment — was well below expectations.

Borsch had predicted a loss ratio of 84.3% for the period, but Aetna’s came in at 83%. The analyst also said Aetna introduced its first meaningful dividend of 60 cents a share.

“The strong guidance is in contrast to” the previously announced third-quarter outlook for commercial-member enrollment to decline by 550,000 to 600,000 during the 2011 first quarter, Borsch said.