The disclosure was made during the latest briefing given by the agency, which is under siege for, among other things, failing to inspect a plant in China that supplied the active ingredient for Baxter’s Heparin, a blood thinner that has been linked to nearly 800 serious side effect reports and at least 19 deaths in the US.

In a teleconference call this afternoon, FDA deputy commmish Janet Woodcock, who heads the agency’s drug review center, calls the contaminant a ‘Heparin-like compound’ and say that it accounted for anywhere between 5 percent and 20 percent of the active pharmaceutical ingredient and finished product tested. However, she adds that, while there is an association, there is “no direct causal link between the contaminant and the adverse events.”

“We don’t know if it was introduced (into the Heparin manufaturing process) by error, the biological process or if it was done deliberately. We’re investigating all the possibilities,” says Woodcock, adding that it’s not clear whether the contaminant was introduced in China or Wisconsin. Baxter’s ingredient supplier, Scientific Protein Laboratories, has facilities in Wisconsin and in China, where it co-owns a plant.

However, Woodcock declined to say whether the contaminant was found at any other plant that may have manufactured the same active ingredient. Baxter now receives its key Heparin ingredient from American Pharmaceutical Products. FDA commish Andy von Eschenbach, who was also on the calls, adds that test kits are going to be used now to look for such problems.

Last month, a Baxter spokeswoman said the drugmaker detected unspecified differences between some lots of the ingredient, but didn’t say whether the lots had come from China or from SPL’s Wisconsin plant, which Scientific Protein owns. Those differences didn’t turned up in routine testing Baxter performs on active ingredients, but she said Baxter used “advanced testing techniques” to find the differences. She added that it was unclear whether the finding was significant.

By the way, the FDA also defended its track record in inspecting plants by saying more than 1,000 inspections were made in fiscal year 2007 - which was described as a record number for overall drug inspections. The agency has been criticized for failing to inspect a sufficient number of plants.