U.S. President-elect Donald Trump, right, introduces retired Marine Corps Gen. James Mattis as his choice for secretary of defense in December. (Gerry Broome/AP)

Retired Marine Gen. James N. Mattis has resigned from the board of the beleaguered Silicon Valley blood-testing company Theranos, according to a person with direct knowledge. Mattis stepped down in December in preparation for a confirmation hearing as President-elect Donald Trump's pick for secretary of defense, the person said.

Theranos referred questions about Mattis's status on its board to the Trump transition team.

“Should Gen. Mattis be confirmed he will resign his positions with all outside entities, as is standard practice,” Trump transition team spokeswoman Alleigh Marre said in an email.

Mattis's name no longer appears on Theranos's Web page listing its board of directors. The Wall Street Journal first reported that Mattis had stepped down from the board.

While leading the U.S. Central Command, Mattis met Elizabeth Holmes, the chief executive of Theranos, at a Marine Memorial event in 2011. He became interested in testing the company's rapid, low-volume blood-testing technology in Afghanistan, an innovation that promised to revolutionize the industry.

Emails obtained by The Post through a Freedom of Information Act revealed that, in the years before he joined the company's board, Mattis pushed for the military to test Theranos's technology in the field.

“I’ve met with my various folks and we’re kicking this into overdrive to try to field your lab in the near term,” Mattis wrote to Holmes in June 2012. “Please don't hesitate to call me or to send an email if you sense that we need to talk.”

Ultimately, experts within the military flagged concerns about the company's regulatory strategy. Holmes complained in an email to Mattis that a military official had misrepresented information about her company to regulators and asked him to intervene. Mattis met with representatives of the military and the Food and Drug Administration, who explained the compliance problems with Theranos's approach. The Afghanistan field test never happened.

Shortly after he retired from the military in 2013, Mattis joined Theranos's board of directors.

He remained on the board as the company, a Silicon Valley darling, fell from grace after regulators uncovered a slew of problems. In 2015, the company stopped using its proprietary finger prick tests for all but one of its blood tests. The Food and Drug Administration found that its “nanotainers” used to collect blood were unapproved medical devices. Last year, federal regulators uncovered a slew of problems at the company's Newark, Calif., laboratory and imposed sanctions on the company and on Holmes, who has been banned from owning or operating a laboratory for two years. The company is appealing that decision. However, in a major blow, Walgreens announced it would terminate its partnership with the company last year. In October, Theranos announced it would lay off 340 employees and shutter its clinical labs and wellness centers.

Mattis remains on the board of directors of General Dynamics, an aerospace and defense company.

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