Health insurer WellPoint Inc said on Wednesday that its fourth-quarter net profit had risen to $464.2 million, or $1.51 per share, helped by an income tax settlement and investment gains.

The company, which bought smaller Amerigroup in December and included its results for the first time, said it had 36.1 million members as of December 31, up 5.5 percent from a year earlier.

Excluding the tax settlement, investment gains and other special items, the company said earnings had increased to $1.03 per share from 99 cents a year earlier, driven by cost controls and operating results.

The company said it expected a 2013 net profit of at least $7.60 per share, including costs of integrating Amerigroup. Analysts on average have been expecting $7.98, according to Thomson Reuters I/B/E/S. It was not immediately clear if the two numbers are comparable.

WellPoint said it was being prudent about its outlook, given the "fluid and dynamic" market over the next 18 to 24 months. It said it expected membership to drop in 2013 to a range of 35.3 million to 35.5 million.

The company is preparing for one of the last major initiatives of U.S. healthcare reform later this year. Under the Affordable Care Act, state and federal health exchanges will start selling insurance to individuals and small groups on October 1.

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