A congresswoman’s relentless questioning has succeeded in getting a Centres for Disease Control and Prevention chief to agree to free coronavirus testing for all Americans.

In a tense standoff, Democrat Katie Porter first quizzed Department of Health and Human Services official Robert Kadlec on the cost of a coronavirus test for an uninsured American.

“I did the math,” she declared as she held up a whiteboard showing the cost of everything from a flu test, to the diagnostic test and hospital visit totals about $1,331.

Ms Porter claimed 40 per cent of Americans cannot afford a $400 unexpected expense – and that a fear of the costs is keeping people from getting tested for Covid-19.

The representative for California then began grilling CDC director Dr Robert Redfield on a statute that states the CDC director “may authorise payment for the care and treatment of individuals subject to medical examination, quarantine, isolation and conditional release”.

She asked: “Dr Redfield, will you commit to the CDC, right now, using that existing authority to pay for diagnostic testing, free to every American, regardless of insurance?”

Dr Redfield began saying the CDC was “going to do everything to make sure everybody can get the care they need”, but he was cut off by Ms Porter stating: “Nope, not good enough. Reclaiming my time.”

After being asked a third time, the health chief appeared to finally concede, replying: “I think you’re an excellent questioner, so my answer is yes.”

“Excellent. Everybody in America hear that – you are eligible to go get tested for coronavirus and have that covered, regardless of insurance,” said Ms Porter.

It is unclear whether Dr Redfield was referring to the test for Covid-19 alone, or for the total cost of everything involved, including a hospital stay.