President Donald Trump revealed Monday that he had undergone an MRI scan during a recent checkup at Walter Reed National Military Medical Center but has remained tight-lipped about what prompted the examination, leading to one medical expert raising serious questions as to the president’s health.

“It's not part of a routine screening examination,” said Dr. Jonathan Reiner, a CNN medical analyst who’s certified in interventional cardiology and internal medicine, speaking on the network Monday.

“There's been really a lack of candor coming from the White House about this," Reiner added. "When they announced that the president would visit Walter Reed at the beginning of this month, they initially said it was for his annual checkup, but when they were reminded that that's not due until April, they said 'okay, it's for a routine semi-annual checkup.'”

Trump revealed the surprise medical visit while aboard Air Force One on his way to Japan and called the MRI scan he received “perfect.” At 79 years old, Trump is the second-oldest president to ever hold office – behind only former President Joe Biden – with questions having been raised about his health after photographs of his hands and ankles have shown bruising and swelling, respectively.

Trump’s most recent visit and MRI scan was done on Oct. 10, his second exam since taking office in January. While the White House described the visit as routine, Reiner said there was nothing routine about receiving an MRI scan, adding that Trump's refusal to elaborate on the visit only degraded trust among Americans.

“The big question is what prompted his MRI?" Reiner said. "What symptoms were they concerned about, what particular type of MRI was performed? Was it a brain MRI, was it a cardiac MRI, was it an MRI of the spine, of his prostate... what prompted the concern that would take him in a relatively unscheduled way to Walter Reed for this testing?”

“Why won't they tell us exactly what was tested, why the testing was performed, and the results?" the physician added. "I think without that, there's really no trust. Just tell the public what's going on with the president!”

Reiner also noted that the White House has its own “prodigious testing capacity,” and that the only reason Trump would seek care outside the White House would be to receive more advanced treatment such as a CT scan or an MRI, something he again noted was not “routine,” contrary to the White House’s statement.