Theranos CEO Elizabeth Holmes at WSJLive 2015. WSJ Theranos CEO Elizabeth Holmes has a net worth of zero dollars, according to Forbes, the go-to publication for assessing the wealth of the world's billionaires.

Theranos, the troubled blood-testing startup, last month voided two years' worth of blood-test results from its flagship Edison machines. This is just the latest in a series of blows for the company, which began with a high-profile exposé from The Wall Street Journal last year that called the company's underlying technology into question.

How did Forbes arrive at the $0 number?

Here is the methodology:

FORBES spoke to a dozen venture capitalists, analysts and industry experts and concluded that a more realistic value for Theranos is $800 million, rather than $9 billion. That gives the company credit for its intellectual property and the $724 million that it has raised, according to VC Experts, a venture capital research firm. It also represents a generous multiple of the company’s sales, which FORBES learned about from a person familiar with Theranos' finances.

Based on this, Forbes concluded that Holmes' 50% stake in Theranos was worth nothing. This is because she owns common stock and would get paid out after investors who own preferred shares, according to VC Experts. So even if Theranos were liquidated, she would be unlikely see any of that $800 million.