Fannie Mae said it will hold a conference call on Friday to answer accounting questions, after Fortune magazine reported that the U.S. mortgage lender may be camouflaging credit losses.

The online Fortune report said Fannie Mae had changed the way it calculates its bad loans, a move that could mask the level of its credit losses.

The news sent fears through investors who sent the stock down 10 percent, wiping out roughly $4.68 billion from Fannie's market capitalization. The stock closed at $43.04 on the New York Stock Exchange. Since the beginning of October, shares have lost about 31 percent of their value.

A Fannie Mae spokeswoman on Thursday declined to comment on the Fortune report but said the company had organized the call in response to queries.

Investors and analysts have been calling with follow-up questions and the appropriate way to deal with this was to schedule a call, she said.

Fannie Mae said last week that its third-quarter net loss doubled from a year earlier to $1.52 billion, as slumping home prices and a credit squeeze drove down values of mortgage securities.

It reiterated a previous forecast for its credit-loss ratio to be in a range of 4 to 6 basis points this year, and said it expected that to rise to 8 to 10 basis points in 2008.

Earlier this week, New York Attorney General Andrew Cuomo said he had served subpoenas on Fannie and Freddie Mac (FRE.N: Quote, Profile, Research) as part of an investigation into inflated home appraisals.

On Friday, Wells Fargo & Co Chief Executive John Stumpf said he believed the nation's housing slump is the worst since the Great Depression and is far from over.

In December, Fannie finished a $6.3 billion restatement of past earnings begun after accounting irregularities came to light in late 2004.

Friday's call will start at 9:00 a.m. Eastern Time, and Chief Financial Officer Stephen Swad and other executives will take questions, the company said.

(Additional reporting by Ilaina Jonas)

(Reporting by Ritsuko Ando; editing by Gary Hill)