Abbott Laboratories failed to follow good manufacturing practices at a plant that makes diagnostic tests, U.S. regulators said.

The Abbott Molecular facility in Des Plaines lacked standard procedures for evaluating finished tests, preventing errors and controlling materials that didn't meet specifications, according to a warning letter dated Aug. 12 and posted today on the Food and Drug Administration's Web site.

"We've already taken a number of steps to address items outlined in the letter," said Don Braakman, a spokesman for the Libertyville Township-based company, in a phone interview today. "We're currently in the process of communicating those specific actions to FDA."