Austin controversially kept US President Joe Biden in the dark about his prostate cancer diagnosis for weeks, while the commander-in-chief and Congress were not told until days after he was hospitalized on January 1 for complications from his treatment.

"Nothing examined during this review demonstrated any indication of ill intent or an attempt to obfuscate," the Pentagon said in an unclassified summary of a review ordered by Austin's chief of staff into the circumstances surrounding his hospitalization last month.

However, "medical privacy laws prohibited medical providers from candid sharing of medical information with the secretary's staff," who were also "hesitant to pry or share any information that they did learn," the review found.

The summary also said there was an "absence of an established methodology for making... an unplanned decision" to transfer authorities from the secretary to his deputy, which "may have contributed to the lack of comprehensive information sharing about the situation.

Austin, a 70-year-old career soldier, initially underwent minor surgery to treat the cancer on December 22, returning home the following day.

But he was readmitted due to complications including nausea and severe pain on January 1.

The White House was not informed about Austin's hospitalization until January 4, while Congress was not told until the following day, and Biden did not learn of the cancer diagnosis until January 9.

Various Republican lawmakers called for Austin -- who apologized earlier this month for the secrecy surrounding his treatment -- to be sacked, but Biden has stood by him.

The defense secretary was hospitalized again on February 11 and treated under general anesthetic for bladder issues.

The public informed around two hours after the fact and the Pentagon said that military, White House and congressional officials had all been notified. Austin was released from the hospital two days later.