At a time when the Trump administration is facing intense criticism for its failure to make coronavirus tests available to millions of nervous Americans, remarks by a federal health official on Tuesday appeared to suggest that the World Health Organization’s diagnostic tests were wildly inaccurate.

In a somewhat rambling answer to a question related to W.H.O. tests, Dr. Deborah Birx, the White House coronavirus response coordinator, said: “It doesn’t help to put out a test where 50 percent or 47 percent were false positives. Imagine what that would mean to the American people. Imagine what that would mean to tell someone they were positive when they weren’t.”

It was not clear where Dr. Birx got those figures, but obviously such an inaccurate test would be worthless. Late on Tuesday night, Dr. Birx confirmed that although she was responding to a question about the W.H.O. test, she was referring to a study of an early diagnostic test used in China.

The paper found that, in a specific subset of those tested in China — asymptomatic contacts of known cases — the tests wrongly found them to be positive 47 percent of the time.