(CNN) Two leading Democratic senators want answers from Aetna Chairman and CEO Mark Bertolini after a former medical director admitted under oath that he never read patients' medical records.

Ron Wyden of Oregon, the ranking member of the Senate Finance Committee, and Patty Murray of Washington, the ranking member of the Senate Health Committee, fired off a joint letter to Bertolini this week, saying the medical director's comments raise serious concerns about Aetna's claims review process and whether the insurance giant has broken federal law. They asked the company to respond to the letter by March 20.

"Using medical records is a fundamental responsibility of health insurers when they review health claims," Wyden said in a statement. "Something is gravely wrong if a leading insurance company is failing to use this basic information at the expense of families' health and peace of mind."

Murray told CNN: "I am hopeful we will receive a thorough and timely response from Aetna."

Aetna said it looks "forward to responding to Senators Murray and Wyden, and will do so before their deadline."

Aetna has lashed out since the story first published, saying the comments in the deposition were "taken out of context" and that "medical records were in fact an integral part of the clinical review process."

In the videotaped deposition, Dr. Jay Ken Iinuma, who served as medical director for Aetna for Southern California from March 2012 to February 2015, said he never looked at patients' medical records during his tenure. The doctor also said he was following Aetna's training, in which nurses reviewed records and made recommendations to him.

"Dr. Iinuma stated that while he was employed as an Aetna medical director, he had never personally reviewed the medical records of any claimant when making claims determinations," Wyden and Murray said in the letter to Bertolini. "Aetna's appeals process may not have been in compliance with federal law."

In the days after CNN first published the story, the insurer released a new sworn statement by Iinuma in which he said he looked at relevant portions of patients' records, just not their entire records. The new statement came nearly a year and a half after his deposition under oath.

Wyden and Murray blasted the insurance provider, saying that such issues "are apparently not new for Aetna."

"In 2009, Aetna Health, Inc., and Aetna Life Insurance paid a $256,000 fine to Arizona insurance regulators for, among other things, 'denying health care provider payments without requesting additional information that could prove the claim valid,' " the senators said.

Wyden and Murray gave multiple issues for the Aetna CEO to address: "Please provide a written description of Aetna's claims review process, including the specific responsibilities of medical directors, nurses and chief medical officers, as well as any other company employees who are involved in such decisions."

Also, the letter says, "Please provide the total number of medical claims Dr. Iinuma reviewed, and the number for which he made determinations, during his tenure as medical director, and note how many were approved and how many were denied."

The senators also asked for the total number of medical directors at Aetna over the past five years and the total number of claims they reviewed, "noting how many were approved and how many were denied, for each of the past five years."

The senators sought guidelines and training materials related to medical directors and their communication with nurses.

Aetna is the United States' third-largest insurance provider, with 23.1 million customers.

Wyden and Murray raised questions about the former medical director's latest sworn statement and asked Aetna's CEO to provide a "detailed timeline and explanation of how this statement came to be, e.g. did Aetna solicit this statement, if so by whom and when? What, if any, legal, financial or contractual relationship between Aetna and Dr. Iinuma existed at the time this statement was made and exists today?"

The deposition by Aetna's former medical director came as part of a lawsuit filed against the company by a college student with a rare immune disorder.

Gillen Washington, 23, is suing Aetna for breach of contract and bad faith, saying he was denied coverage for an infusion of intravenous immunoglobulin when he was 19. His suit alleges that Aetna's "reckless withholding of benefits almost killed him."

Aetna has rejected the allegations, saying Washington failed to comply with its requests for blood work.

Washington, who was diagnosed with common variable immunodeficiency in high school, became a new Aetna patient in January 2014 after being insured by Kaiser.

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Aetna initially paid for his treatments after each infusion, which can cost up to $20,000. But when Washington's clinic asked Aetna to pre-authorize a November 2014 infusion, Aetna says it was obligated to review his medical record. That's when it saw his last blood work had been done three years earlier for Kaiser.

Despite being told by his own doctor's office that he needed to come in for new blood work, Washington failed to do so for several months, until he got so sick that he ended up in the hospital with a collapsed lung.

Once his blood was tested, Aetna resumed covering his infusions and pre-certified him for a year. Despite that, according to Aetna, Washington continued to miss infusions.