The US Food and Drug Administration has announced that it has identified the mysterious substance which contaminated  some lots of the recalled blood-thinner heparin sold by Baxter International Inc. It is a man-made chemical compound known as over-sulfated chondroitin sulfate which is much cheaper than heparin.

"Right now, people should not be alarmed," said Dr. Janet Woodcock, director of the FDA's Center for Drug Evaluation and Research. "We have not received any more reports of fatalities of this type since the recall on Feb. 28."

It appears that heparin was cut with the similar substance to reduce costs. "It doesn't appear to be a natural contaminant that got in there. We don't know how it was introduced or why," Woodcock said. This is further reinforced by the fact that the chondroitin sulfate was modified to mimic heparin. Normal chondroitin sulfate is used as a supplement by people suffering from joint problems.

Heparin, made from ingredients extracted from pig intestines, is used to prevent blood clots in millions of people with heart conditions, kidney disease and in surgery. The contaminant made up between 2 and 50 percent of the heparin samples tested by the FDA, which did not assert directly that the heparin was counterfeited on purpose.

However, "A child could tell you it's counterfeiting," claims a Professor of pathology and pharmacology at Loyola University Chicago, Dr Jawed Fareed in an interview with the NY Times.

Last month, Baxter first recalled nine lots of the heparin after receiving hundreds of reports of allergic reactions possibly linked to heparin, as well as reports of four deaths. Shortly after, the company recalled all remaining heparin products. The other major U.S. heparin supplier, APP Pharmaceuticals Inc, ramped up production to avoid a drug shortage after the Baxter recall. Tests on APP's heparin have not turned up any contamination.