Tribune -- The U.S. Food and Drug Administration, for the first time, has conclusively linked deaths of patients infused with the blood thinner heparin to a foreign substance found in specific lots of the drug made by Deerfield-based Baxter International Inc. In an interview Tuesday with the Tribune, the FDA said it completed its review of 93 death reports related to heparin that the agency received from Jan. 1 to March 31, a period when there was a dramatic spike in potentially deadly allergic reactions from patients who had been injected with heparin. The popular blood thinner is used widely in large dosages, often before patients have dialysis or heart surgery.