SALT LAKE CITY (AP) — A Utah prison inmate is dead of an apparent heart attack related to renal failure after a dialysis provider didn't show up for a scheduled treatment for two days in a row, a prison official said Tuesday.

Ramon C. Estrada, 62, was set to be paroled in less than three weeks when he died Sunday at the prison in Draper, Utah Department of Corrections spokeswoman Brooke Adams said in a statement Tuesday afternoon.

He was scheduled to have dialysis Friday at the prison's treatment center, but a technician did not show up on Friday or Saturday. The technician or technicians involved worked for a University of Utah Hospital clinic that provides dialysis for the prison.

Kathy Wilets, a University of Utah Hospital spokeswoman, said there appears to have been some miscommunication with South Valley Dialysis technician scheduling, and the hospital is investigating.

"We have a responsibility to provide quality care for patients. We will now conduct a thorough review of the circumstances that led to this unacceptable mistake and will take whatever steps are necessary to improve communications and procedures," Wilets said in a statement.

The organization was saddened to learn of Estrada's death, she said.

Adams said six other inmates had been waiting for dialysis treatment and were taken to a hospital for evaluation. Four of them were treated, and one of the four remained hospitalized Tuesday afternoon. The other two inmates were returned to their cells. Adams did not have details about how long the four admitted to the hospital went without dialysis treatment.

The Utah State Medical Examiner's office will conduct an autopsy on Estrada's body and determine his cause of death, Adams said.

The corrections department's law enforcement bureau is investigating, but an initial review indicates that Estrada's lack of treatment may have played a role in his death, Adams said.

The prison's clinical services director has been placed on leave as the department investigates how prison staff and South Valley Dialysis responded and how a similar situation can be prevented.

The department is taking immediate steps to ensure the prison has contact numbers for technicians scheduled to show up and that prison staff are notified when technicians show up for treatment and that they report on inmate conditions, Adams said.

Adams said she did not have details about whether prison staff tried to contact the technicians when they failed to show. She told The Associated Press that was part of the ongoing investigation.

The Unified Police Department, which covers Salt Lake County, is also investigating.

Unified Police Lt. Justin Hoyal said investigators are waiting for autopsy results to pinpoint the cause of death, but didn't find any signs of foul play in the man's cell.

Estrada had been in prison since August 2005 on a rape conviction, Adams said. He was scheduled to be paroled on April 21.

Estrada was from Mexico and believed to have been in the country illegally, Adams said. He would have been turned over to the U.S. Marshals Service when his sentence was complete, she said.

Randall W. Richards, a lawyer who represented Estrada in 2005, did not return messages seeking comment Tuesday. It was unclear if Estrada had an attorney at the time of his death.

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Associated Press writer Lindsay Whitehurst in Salt Lake City contributed to this report.