A Citigroup analyst on Friday cut her rating on Invitrogen Corp., after the maker of laboratory research products reported lower-than-expected results for the third quarter and issued disappointing guidance.

Invitrogen on Thursday said it swung to a third-quarter loss due to a charge, but booked $311 million in revenue, in line with consensus estimates.

Excluding the charge, but including stock-option expense, the company earned 72 cents per share, while analysts polled by Thomson Financial were expecting higher profit of 78 cents per share. In a conference call, the company guided for a fourth quarter similar to its third-quarter performance.

Citigroup analyst Elise Wang in a client note cut her rating to "Hold" from "Buy" and slashed her target price to $68 from $86.

"All else equal, we would be buyers if the stock drops into the low to mid-$50s range," wrote Wang.

The Wall Street estimate for fourth-quarter revenue is $337.8 million, much higher than the $311 million the company implied.

She said Invitrogen's disappointing guidance stems from lower margins of 58 percent, compared with the analyst's 62 percent forecast, due to manufacturing variances and an unfavorable product mix.

"Furthermore, although the company indicated it has nearly completed its strategic review of its business, management did not provide sufficient clarity on the potential steps it may take to improve next year's outlook given recent operating margin pressures," Wang wrote.