company said it expects public health plan membership to continue growing due to the weak economy, potentially cutting into profit because of higher medical claims.

The company said it is not issuing 2009 guidance.

The stock lost $2.55, or 8.8 percent, to $26.46 in afternoon trading. Shares have traded between $16.02 and $32.40 over the last 52 weeks.

The Virginia Beach, Va.-based company said it expects membership in public health plans such as Medicare and Medicaid to continue growing significantly. That, in turn, could continue elevating medical costs, potentially cutting into the company's profit. New members typically incur higher medical costs through the first three to six months, the company said.

"While there may be pressure on outpatient medical cost trends during the year, management believes it is premature to draw any conclusions regarding full year 2009 earnings per share results in light of the range of other factors that impact financial performance within the year," the company said, in a Securities and Exchange Commission filing Tuesday.

Amerigroup expects to provide an update on costs and other items when it releases second-quarter financial results July 31.

J.P. Morgan reaffirmed a "Neutral" rating on the stock, but cut its target price to $30 from $33.