This is the VOA Special English Health Report.

　　Heparin is a blood-thinning medicine made from pig intestines, which often come from small farms in China. The drug is often used to prevent blockages during kidney dialysis treatment and different operations.

　　But in February, a major producer, Baxter International, recalled almost all of its heparin. Tests showed the presence of a chemical called oversulfated chondroitin sulfate. This is chemically similar to heparin but should not have been used. Who added it, and why, remains unclear.

　　Officials in the United States have received hundreds of reports of severe reactions, including deaths.

　　On April twenty-first, the Food and Drug Administration released a warning letter to a Chinese supplier for the Baxter heparin. The letter said Changzhou SPL had received material from an unacceptable supplier, and could not purify the materials used to make the drug. F.D.A. inspectors found that the company did not follow good manufacturing practice.

　　Chinese officials have suggested that the contaminant entered the heparin during the finishing process in the United States. Baxter disagreed. A Chinese delegation visited a Baxter factory in New Jersey last week.

　　Scientists have offered explanations for how the chemical could have caused the allergic reactions and low blood pressure seen in patients.

　　Reports from two teams were published online last week in the New England Journal of Medicine and Nature Biotechnology. Both teams were led by Professor Ram Sasisekharan at the Massachusetts Institute of Technology.

　　Officials in the United States are investigating eighty-one deaths in heparin patients with signs of allergic reactions or low blood pressure. Most of these deaths happened between November of last year and February of this year. But F.D.A. officials say the reactions may not have been the cause of death in all cases.

　　China says there is no proof of a connection between the contaminant and the deaths. The chemical has been found in heparin supplies in other countries. But Chinese officials note that the United States and Germany are the only countries that have reported any health problems.

　　The widespread use of foreign drug suppliers has led American lawmakers to call for at least five hundred additional F.D.A. inspectors. Also, a House subcommittee held a hearing Tuesday called "The Heparin Disaster: Chinese Counterfeits and American Failures."

　　And that’s the VOA Special English Health Report written by Caty Weaver. I’m Barbara Klein.