A global manhunt launched by Johnson & Johnson has tracked to China counterfeit versions of an at-home diabetes test used by 10 million Americans to take sensitive measurements of blood-sugar levels.

Potentially dangerous copies of the OneTouch Test Strip sold by J&J’s LifeScan unit surfaced in American and Canadian pharmacies last year, according to federal court documents unsealed in June. New Brunswick, N.J.-based J&J, the world’s largest consumer-health products maker, learned of the counterfeit tests after 15 patients complained of faulty results last September.

Tipped off by J&J, the U.S. Food and Drug Administration issued a nationwide consumer alert in October without disclosing the link to China. While no injuries were reported, inaccurate test readings may lead a diabetic to inject the wrong amount of insulin, causing harm or death, the agency said. Fake medicines are a $32 billion global business, says the World Health Organization, and the FDA says it ran 54 counterfeit investigations in 2006, almost double the year before.

The court filings disclose, for the first time, that China is the source of about 1 million phony test strips that have turned up in at least 35 states and in Canada, Greece, India, Pakistan, the Philippines, Saudi Arabia, and Turkey.

“The source was from China, through Canada, to the United States,” said Steven Gutman, director of the Office of In Vitro Diagnostic Devices and Evaluation at the FDA in Rockville, Md. “As far as we can tell, the counterfeiter has been put out of business in the U.S.”

The court documents show, also for the first time, a worldwide distribution chain discovered in the past year by investigators hired by Johnson & Johnson. The trail, initiated by consumer complaints to a LifeScan hotline, first led detectives to 700 pharmacies where the products were sold, then to eight American wholesalers, and then to two importers, one in America, who was tracked down in a hotel room in Las Vegas, and another in Canada.

Records seized from the importers show the counterfeit strips were bought from Henry Fu and his company, Halson Pharmaceutical, which according to its Internet site is based in Shanghai.

“When we started down this road, we had one box of product,” Geoffrey Potter, the lead lawyer for J&J, told the U.S. District Court in Brooklyn. “The box looked like a counterfeit $100 bill looks, perfect. They were made of parts we don’t have in our factory.”

On October 13, the FDA published a consumer alert and LifeScan issued a press release and notified pharmacists, distributors and wholesalers to watch for packages with four separate lot numbers. Patients place blood from a finger prick onto the strip and insert it into a plastic test device that looks somewhat like a hand calculator. The results help patients make sure the right amount of insulin is used to keep glucose, or blood sugar, from rising to dangerous levels.

As diabetics without insurance may spend $100 to $200 a month for the strips, pharmacies with low-income customers are tempted to buy discounted tests from gray market distributors. The American and Canadian defendants say they believed the counterfeit strips were lower-priced gray market products diverted from normal distribution channels.