It often takes more than two years for Correctional Service Canada to complete a mandatory review when someone behind bars dies of natural causes, the national prison ombudsman says.

A report released Monday by correctional investigator Howard Sapers also raises questions about the quality and level of care provided to prisoners before they die in custody.

Sapers says he uncovered questionable diagnostic practices, incomplete records, lax information-sharing and delays or lack of follow-up on treatment recommendations.

In addition, prison staff did not investigate the circumstances of natural deaths beyond recording the cause as either unexpected or sudden.

Correctional Service's process for reviewing such in-custody deaths failed to generate significant findings or recommendations, Sapers says. There is no way of determining whether a death was preventable or premature.

On average, about 35 federal prisoners die each year for natural reasons — by far the most common cause, the report says.

"More offenders are growing old in custody and succumbing to chronic disease in prison."

It calls on the prison service to do a comprehensive "lessons-learned exercise" to identify measures to reduce or prevent natural cause deaths.

Sapers recommends several other changes:

All sudden or unexpected fatalities should be subject to a full national board of investigation — the kind of inquiry that now happens when there's a suicide or homicide.

The board should convene within 15 working days of the fatality.

All reviews of prison deaths — no matter the cause — should be led by a doctor.

Death review reports should be shared with family members in a timely way.

The process for reviewing deaths in prison should also be subject to a "quality control audit" by an outside medical examiner, Sapers says.

In preparing the report, the ombudsman's office hired an independent doctor to study the medical care provided to a sample of 15 offenders before they died. All of the deaths involved men and all but one was anticipated by the prison service.

In each case, the doctor looked at the same medical charts, files and records that were part of Correctional Service's case review.