Walgreens will halt opening any new Theranos testing centers until the start-up "resolves questions about its technology," according to The Wall Street Journal.

The drugstore chain already has 41 stores in Arizona and California, but an official told The Journal that there are "no concrete plans at this stage" to grow that number.

Theranos, which touts a new approach to blood testing, has come under scrutiny after an investigative story in The Journal reported that it relies heavily on traditional technology versus its proprietary blood tests. Those tests later had their functionality called into question.

Theranos, which has raised about $400 million at a $9 billion valuation, called the original WSJ report "full of falsehoods." But it's reportedly stopping most of its signature blood tests under pressure from federal regulators.

Melia Robinson, a Tech Insider reporter, tried to get her blood drawn from a Walgreens Theranos center in California over the weekend, but it was closed because the computer system was down.

"With the completion of our Phoenix rollout that was part of our current agreement with Theranos, we are currently in discussions about the next phase of our relationship. Plans to open more Theranos Wellness Centers are dependent upon both companies' ability to reach a mutually beneficial arrangement," said Walgreens spokesman Michael Malzin.

The testing centers have remained open, he confirmed.

We've reached out to Theranos for comment, and we'll update when we hear back.