US business magazine Forbes, which monitors the world’s wealthiest individuals and publishes a rich list, has revised the net worth of the woman it named as America’s richest self-made woman last year from $4.5bn (£3.1bn) to zero.

Forbes said its estimate of Elizabeth Holmes’s wealth was based entirely on the 32-year-old’s 50% stake in troubled blood-testing startup Theranos.

The company acknowledged in April that it is 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.

Theranos said the WSJ articles were inaccurate when they were published.

Forbes says its previous estimate of Holmes’s wealth came from a $9bn valuation for the private company in 2014.

Holmes started Theranos in 2003 and remains its chief executive.