An Arizona lab run by blood-testing firm Theranos Inc. put patients at risk and failed to quickly fix its deficiencies, the main U.S. lab regulator found, triggering a new round of sanctions last month against the company.

The Centers for Medicare and Medicaid Services imposed some of the harshest penalties in its arsenal on the Arizona lab. The agency revoked the lab’s U.S. testing license, barred it from billing Medicare and ordered it to alert customers of its problems, according to a Jan. 27 letter obtained by The Wall Street Journal in a public records request.

It is the second lab operated by the Silicon Valley startup to face that penalty in less than a year. Regulators pulled the license of Theranos’s main California lab in July, a penalty the company is appealing. Theranos shut down both its California and Arizona labs in October, saying it would exit the testing business to focus to developing novel lab equipment.

A Theranos spokeswoman said the firm “continues to work with CMS to resolve this matter and appreciates the agency’s ongoing collaboration.”

In November, Theranos founder Elizabeth Holmes wrote to regulators that the firm was committed to addressing “any negative patient impacts that may have resulted from shortcomings at the Laboratory,” according to a copy of the letter reviewed by the Journal.