DEERFIELD, Ill., Feb. 29 (UPI) -- Baxter International Inc. (NYSE:AX) has recalled the remaining supplies of its blood-thinner heparin, completing a recall they announced in mid-January.

Baxter recalled nine lots of the drug and ceased production in January on reports of more than 400 allergic reactions including stomach problems and blood pressure declines. The New York Times (NYSE:NYT) reported the Food and Drug Administration believes 21 people might have died from heparin, which is used during surgery and dialysis as a blood thinner, but is not absolutely certain.

The FDA hasn't found the "root cause" of the problems tied to Baxter's heparin, Sandra Kweder, an FDA deputy director, told The Washington Post. U.S. federal inspectors have said they found possible deficiencies at a Chinese plant supplying the active ingredient in Baxter's product, but are not certain they are responsible for the problems.

The FDA is also investigating two companies that supplied crude heparin to Changzhou SPL, Baxter's supplier, the Times reported. Crude heparin is made from scraping the mucous membrane from the insides of pigs' intestines.

In January Baxter did not recall heparin already in circulation because of a supply shortage but Thursday Baxter said "the FDA has now concluded that there is sufficient capacity on the part of other suppliers that Baxter's recall will not jeopardize access to this drug," the Chicago Tribune reported.

APP Pharmaceuticals Inc. (NASDAQ:APPX), the other major U.S. supplier, has increased its production in response to the situation.