WASHINGTON — A Peace Corps doctor caring for a gravely ill volunteer in China ignored a fellow physician’s warnings that the volunteer needed intravenous fluids “in 30 minutes or he is going to die,” and altered her notes about his treatment after submitting them to headquarters for review, according to a confidential report by the agency’s independent watchdog.

In a detailed examination of the death of Nick Castle, a 23-year-old volunteer who was the subject of an article in The New York Times in July, the Peace Corps inspector general cited “cascading delays and failures in the treatment” of Mr. Castle as a factor in the death, and said the Peace Corps doctor, Jin Gao, had “failed to use prudent judgment.”

Dr. Gao resigned in September and could not be reached for comment. The agency had previously said that while Mr. Castle’s death was “a tragic experience,” its own internal review — including an analysis by an outside expert — found that the death, from a gastrointestinal illness, could not have been prevented.

The inspector general’s report, which has not been made public, cites numerous medical lapses strongly suggesting that Mr. Castle’s death could in fact have been prevented, although it does not explicitly blame the Peace Corps.