April 21 (Reuters) - UnitedHealth ( UNH ) opened the first-quarter earnings season for insurers with a strong performance, raising its annual profit forecast and surpassing Wall Street expectations for quarterly earnings and revenue.

The upbeat results boosted shares of the conglomerate, which has faced a series of setbacks over the past two years, including rising medical costs, a cyberattack at its technology unit, and the killing of the head of its insurance unit that sparked a public backlash against the industry.

Below are reactions from analysts and investors.

ANN HYNES, MIZUHO ANALYST

"We believe this was a positive quarter for UNH. Highlighting the quarter was the beat on medical cost trend and the strong performance in Optum Health."

"While medical cost trends remain elevated, this remained in line with the company's expectations, which we view as supportive of our belief that medical cost trend acceleration has peaked."

DAVID WAGNER, HEAD OF EQUITY AND PORTFOLIO MANAGER AT APTUS CAPITAL ADVISORS

"Investors are likely showing signs of relief with this mornings premarket on UNH. The stock has had a volatile run over its last few earnings reports, largely dictated by surging medical costs in its Medicare Advantage business and regulatory shifts. While the stock has struggled for much of the past year, it is currently showing signs of a turnaround, or at least stability that investors are appreciating."

"The highlight of the report for me was the margins."

MICHAEL WIEDERHORN, OPPENHEIMER ANALYST

"Overall, results were strong, as UNH appears poised to return to its consistent beat-and-raise ways. We expect the stock to be strong on this release, which should also support the group."

LANCE WILKES, BERNSTEIN ANALYST

"we had expected guidance raises this year, but had thought Q2 was the more likely first raise. We assume the early raise is likely due to stronger MA performance and possibly improved reserve development from 2025 claims, which would suggest a better jump off point."

"Key questions to understand magnitude of full-year outperformance will be seasonality of MA related results and prior period development."

LISA GILL, J.P.MORGAN ANALYST

"On balance, we see this as a positive first step for UNH... While investors will want a better understanding of the cadence and dynamics at play at Optum, we think this print should broadly start MCO earnings off on the right foot."