With the supply for IV saline making a gradual recovery after manufacturing plants in Puerto Rico battered by Hurricane Maria return to full capacity, a new concern is the shortage of heparin for the U.S. market. The anticoagulant, used heavily by hospitals for multiple applications and by dialysis facilities, is already on the FDA’s list of drug shortages.

U.S. Senate Energy and Commerce Committee leaders sent a letter on Feb. 2 to FDA Commissioner Scott Gottlieb noting “inconsistences and red flags” regarding China’s heparin export market, particularly supplies going to Thailand and Hong Kong that may be cutting into U.S. supplies.

The letter, signed by Energy and Commerce Committee chairman Rep. Greg Walden , R-Ore., Energy and Commerce Committee vice chairman Rep. Joe Barton, R-Tex. Health Subcommittee chairman Rep. Michael C. Burgess, MD, R-Tex., and Oversight and Investigations Subcommittee chairman Rep. Gregg Harper, R-Miss., outlined three areas of concern: 1) whether the Chinese heparin supply is shrinking or increasing, which could affect the risks of a heparin shortage in the United States “and could raise the risk of economically-motivated adulteration,” they wrote; 2) whether Chinese customs data accurately reflect Chinese heparin export and import activity; and 3) whether the recent emergence of significant U.S. heparin imports to China “is further constraining the U.S. domestic supply of heparin,” the legislators wrote.

In 2007 and 2008, more than 100 people died in what was later traced to contaminated heparin imported from China. Despite the United States’ reliance on China’s heparin supply, the United States also exports the drug to China.

“Between 2007 and 2013, the U.S. either had zero exports or exports to China in the single digits. In 2014, the U.S. exported 2,003 kg of heparin to China, and in 2015, the U.S. exported 2,822 kg of heparin to China,” the committee leaders wrote to Gottlieb. “In 2016, the U.S. exported 17,050 kg of heparin to China, by the far the leading exporter of heparin that did not originate in China and with the greatest value of imports at $11,634,209.”

The exports to Thailand and Hong Kong were also unusual, the Congressmen noted, having gone from no exports a decade ago to more than 40,000 kg exported to Thailand and 28,000 kg to Hong Kong in 2016.

“It is not apparent why Thailand and Hong Kong became leading export markets for China,” they wrote in the letter. “Neither location has a large heparin manufacturing presence.”