Silicon Valley darling Theranos has found itself under unpleasant scrutiny after a Wall Street Journal report last week revealed that the company isn't using its headline blood testing technology for most of its customers. The machine, called Edison, is supposed to be able to take all sorts of blood tests with only a small sample from a finger prick.

Now, Theranos' most important partner, Walgreens, wants some answers. An official at the drug store chain, which currently houses "wellness centers" powered by the startup's technology in 41 of its stores, tells the Journal that the company won't be expanding the program for the time being. The partnership gives Theranos a physical presence to compete with other lab testing services.

Theranos has 'wellness centers' in 41 Walgreens locations

Walgreens officials met with Theranos on Thursday, according to The Wall Street Journal, and an official said, "We’re trying to figure out where we are and what we do going forward. We need to understand the truth."

Among other claims, the Journal originally reported last week that the start-up covered up findings during regulatory tests that showed that results from its proprietary Edison machines didn't always match up with those from conventional machines. Theranos vehemently rejected the report this week, saying that the Journal's report was misleading and false.