WASHINGTON — U.S. health officials said Wednesday they have not inspected a Chinese factory that may be a source of problems with a blood thinner linked to allergic reactions and four deaths, but plan an inspection as soon as possible.

The Baxter International blood thinner has been linked to hundreds of reports of allergic reactions and the four deaths. The Food and Drug Administration is investigating.

"While no FDA inspection of the facility has been conducted to date, preparations are being made to perform an inspection as soon as possible," the FDA said in a statement. "We have already requested expedited access to the facility, facilitated through a recently signed agreement with the Chinese State Food and Drug Administration."

The FDA has also requested the facility's inspection data and other reports.

Baxter buys the active ingredient for the drug heparin from a supplier that manufactures it both at the Chinese factory and a facility in the U.S., Baxter spokeswoman Erin Gardiner said.

Baxter inspected both facilities last year and found no quality issues, Gardiner said. However, the company plans to re-inspect the facilities "very soon" as part of its own investigation, she said.

FDA spokeswoman Karen Riley emphasized in an e-mail response to an Associated Press query that the agency has "just begun our investigation, and we don't know the cause of these allergic reactions. It could be any number of things. The active ingredient is only one of the potential suspects we must look at."

Earlier this week, the FDA told doctors to switch from using Baxter's heparin, citing 350 reports of side effects so far this year. Four people died while taking the drug, although the agency said it wasn't clear if the heparin was to blame. In all of 2007, the FDA received 100 reports of problems with the drug.

Last month, Baxter had recalled nine lots of the injectable drug after learning of allergic reactions among dialysis patients, problems ranging from dizziness and fainting to a racing heartbeat. This week, Baxter said it would stop manufacturing multiple-dose vials while it and FDA attempted to locate the source of the problems.

Baxter accounts for about half the U.S. supply of heparin.