UPDATE 1-Aetna quarterly profit beats forecasts as new members surge

(Adds details on customer growth)

April 24 (Reuters) - Aetna Inc said on Thursday that first-quarter net income rose 36 percent as it added people in its Medicare and commercial business, which includes customers from insurance exchanges created under President Barack Obama's signature healthcare law.

Quarterly operating profit grew to $1.98 per share as the percentage the third-largest U.S. health insurer spent on claims declined in its commercial business.

Analysts on average had expected earnings of $1.55 per share, according to Thomson Reuters I/B/E/S. That figure excludes items such as acquisition costs for the purchase of Coventry last year, which also helped profit.

The company reported net income of $665.5 million, or $1.82 per share, up from $490.1 million, or $1.48 per share, a year earlier.

Aetna said it had 22.72 million medical customers at the end of March, up from 22.19 million at the end of December and 18.3 million at the end of March 2013.

The company's commercial business grew by 405,000 during the first quarter, helped by the Jan. 1 start of new commercial coverage under the healthcare reform law.

(Reporting by Caroline Humer; Editing by Lisa Von Ahn)