Former employees of the widely watched Silicon Valley blood-testing startup Theranos Inc. have accused the company of sketchy laboratory and research practices, according to anonymous sources who spoke with the Wall Street Journal for a report published Monday. Theranos has declined to comment on the allegations, saying it has not received copies of any alleged complaints.

The Journal said it reviewed copies of two complaints. One was filed in September with the Centers for Medicare and Medicaid Services (CMS) by a former Theranos lab employee, saying employees were told to keep testing patients with a blood-analysis device known as Edison despite “major” problems with accuracy.

The other complaint, filed earlier this month by a different former employee to the Food and Drug Administration, accused Theranos of requesting regulatory approval for a herpes test based on a study that breached research protocol.

“Agencies have a process for evaluating complaints, and many complaints are not substantiated,” Theranos spokeswoman Brooke Buchanan told the Journal. The company rejects allegations of the veracity of the Edison devices, the company’s in-house blood testing machines and a key component of the company’s services to doctors and their patients.

The complaint to the CMS said the Edison machines would produce “radically different results” for the same patients, citing one instance where a thyroid test would give radically different results for one patient tested twice on the same day.

Theranos was founded in 2003 by then-19-year-old prodigy Elizabeth Holmes, who captured the attention of the medical-testing community for patenting a way to perform multiple tests from a single drop of blood and transmitting the data wirelessly. After a funding round last year that valued Theranos at $9 billion, Holmes, 31, became the country’s youngest female billionaire and the sixth-richest entrepreneur under 40, according to Forbes.