Here's where heparin comes from:

The WSJ's Gordon Fairclough snapped this picture at the Yuan Intestine & Casing Factory, where men "wring pulp from pig intestines, then heat it in concrete vats."

Heparin sold by Baxter International in the U.S. has recently been associated with hundreds of adverse reactions and a few deaths. Scientific Protein Laboratories, Baxter's main supplier of the active ingredient in the blood thinner, says that the Yuan Intestine & Casing Factory isn't in its company's supply chain.

But the company does have a joint-venture that sources raw heparin, which is derived from pig intestines, from a handful of Chinese facilities. It's not clear whether the Chinese operation is the source of the ingredients that seem to be causing harm in patients who receive the blood thinner.

Still, the heparin issue is raising questions over whether heparin makers should be able to track their product back to individual pigs. The drug goes through a complex purification process between pig and person, which some regulators say eliminates the need to identify the source animal. Others argue, though, that even the raw materials should be traceable in order to quickly contain any problems that arise.