Canadian doctors are being urged to stop screening men for prostate cancer using a blood test once hailed as a landmark discovery in early cancer detection.

The Canadian Task Force on Preventive Health Care says PSA screening results in a less than a one per cent reduction in death from prostate cancer and that the harms of screening outweigh the benefits.

The expert panel says most cancers detected by PSA screening are slow growing and not life-threatening, and that as many 56 per cent of all men diagnosed with prostate cancer are over diagnosed — meaning the cancer never would have caused symptoms or killed the man during his lifetime.

Over diagnosis exposes men to needless treatments that can lead to impotence, incontinence and other complications of radiation, surgery and hormone therapy, the federal task force warns in controversial new guidelines published Monday in the Canadian Medical Association Journal.

Within hours of the guideline’s release, critics warned the new recommendations would lead to more cases of advanced prostate cancer. In a statement, Prostate Cancer Canada said early detection “can be the difference between life and death.”

The blanket recommendations against screening are too broad and sweeping and “may do a disservice to Canadian men who are at risk for prostate cancer,” added Dr. Anil Kapoor, a professor of urology at McMaster University and head of the genito-urinary oncology program at the Juravinski Cancer Centre and St. Joseph’s Hospital in Hamilton.

“The Canadian Urological Association feels that it should be individualized, in discussion with the patient,” Kapoor said.

He said the task force ignored other studies that showed a survival advantage with PSA screening.

“Prostate cancer deaths have dropped by 45 per cent since we started screening back in the ’80s,” Kapoor said. “There are patients who would benefit from screening.”

The PSA, or prostate specific antigen test, measures a protein produced by the prostate gland. The higher the man’s blood PSA levels, the more likely he is thought to have cancer. Many doctors recommend an annual PSA starting at age 50.

But even higher-than-normal PSA counts don’t necessarily mean the man has prostate cancer, and cancer can be present even with low PSA levels.

Symptoms of prostate cancer can include weak urinary flow, an urgent need to urinate, frequent urination during the day and especially at night and blood in the urine.

The PSA test was originally designed to help track how men diagnosed with prostate cancer are responding to treatment. But it’s use rapidly spread to include screening healthy men as well.

Before the PSA test, “we didn’t really have anything, except for the digital rectal examination,” said Dr. Neil Bell, chair of the task force’s working group on prostate cancer screening and a professor in the department of family medicine at the University of Alberta.

“It was a nice blood test you could do and hopefully it would tell you that the men you were screening were at risk for prostate cancer or not,” he said. But the test was widely adopted before there was good evidence to back using it as a screening tool.