NEW YORK - Forbes has revised the net worth of the woman it crowned America's richest self-made woman last year from $4.5 billion to nothing.

Forbes says its estimate of Elizabeth Holmes' wealth is based entirely on her 50 percent stake in troubled blood-testing startup Theranos. The company acknowledged in April that it's under investigation by several regulators and agencies following a series of reports by The Wall Street Journal in which former employees said the company's tests were unreliable. The tests use only a few drops of blood.

Theranos said the articles were inaccurate when they were published.

Forbes says its previous estimate of her wealth came from a $9 billion valuation for the company in 2014.

Get Breaking News Delivered to Your Inbox

Theranos, based in Palo Alto, California, has raised millions of dollars by pitching its technology as a cheaper, faster way to run dozens of blood tests. Holmes, reportedly the nation's youngest female billionaire, has said that she founded Theranos in response to her fear of needles. The company's lab tests are pitched as costing a "fraction" of what other labs charge.

But one of the company's partners, Walgreens, asked Theranos in January to stop sending samples collected at its stores to a testing facility that drew regulatory scrutiny over possible patient risks. Walgreens, the nation's largest drugstore chain with over 8,000 stores, said the decision only affected 40 stores in Arizona and one in Palo Alto, California.

Walgreens told Theranos to either send tests to a certified lab in the Phoenix area that Theranos runs or to an accredited third-party lab.

The 32-year-old Holmes started Palo Alto, California-based Theranos in 2003 and remains its CEO.

CBS MoneyWatch reported last month that the blood-testing company is also facing a lawsuit that alleges consumer fraud and false advertising. An Arizona resident identified in the lawsuit as M.P.B. is suing the company, alleging that he purchased the Theranos test under the mistaken belief that the company's Edison blood-testing device would provide accurate results.

In a statement emailed to CBS MoneyWatch, Theranos said the lawsuit "is without merit. The company will vigorously defend itself against these claims."