Walgreens Boots Alliance said it is terminating its relationship with Theranos and closing operations at all 40 Theranos Wellness Centers at its stores in Arizona.

The company, the largest drugstore chain in the United States, said it will be working over the next several days to help transition customers.

Walgreens said it informed Theranos that tests collected at its Wellness Centers at Walgreens stores in Arizona must be sent only to Theranos certified lab in the Phoenix area or to an accredited third-party lab for analysis.

It said no patient samples were to be sent to the Newark lab until all issues raised by Centers for Medicare and Medicaid Services have been fully resolved.

Theranos Inc. was sued in late May and is accused of endangering customer health through "massive failures" that misrepresented the accuracy and quality of its blood tests.

The blood-testing company once touted its Edison device as a ground-breaking technology able to test blood from just a pinprick.

The CMS said in January that Theranos's practices violated several clinical-laboratory regulations, jeopardizing patient health and safety.

Theranos has been in the spotlight after reports in the Wall Street Journal suggested that its blood-testing devices were flawed and had problems with accuracy.