The risk of cancer is measured by looking at the quantity of blood in stools, and is based on a cut-off value of 200ng of haemoglobin (Hb) per ml.
In a letter published yesterday in the New Zealand Medical Journal, the group argued the health and disability commissioner's code of conduct was breached by the current protocol of not showing patients their results, other than "positive" or "negative".
They urged the Ministry of Health to provide more detail.
"[The] numerical result should be provided with explanation of why colonoscopy is, or is not, recommended by the [National Bowel Screening Programme]," the letter said.
Christchurch surgeon Phil Bagshaw, founder of the Canterbury Charity Hospital Trust, said patients could request the exact level if they wanted to, but many did not even think to do that, he said.
They were left in the position where "they don't know that it's anything other than a yes-no answer".
Despite the cut-off being 200ng, a Waitemata pilot study found 17% of all bowel cancer sufferers had a reading of 75ng or below.
"They should know that it's a number," Associate Prof Bagshaw said.
"It's a basic right ... that the patient owns their results. "Really as far as the law is concerned, nobody has a right to keep it from them," he said.
If the result was high, for instance 199ng rather than 200ng, and the patient had a family history of the illness, they could go to their GP who could potentially ask whichever health board the patient fell under to make an exception and get a colonoscopy done.
People who wanted a test done could also go privately, or, in Canterbury, get the procedure done via the Canterbury Charity Hospital Trust.
As well as Prof Bagshaw, Otago preventive medicine Associate Prof Brian Cox, Ainslie Talbot, and Dunedin School of Medicine senior research fellow Dr Mary Jane Sneyd signed their names to the letter.
Prof Bagshaw said Prof Cox had been the force behind the group, discussing the issue with legal experts and ethicists.
The group was spurred into action by " a person who had bowel cancer who brought it to our attention".
Prof Bagshaw said he hoped the letter would generate debate.
"It is an anomaly, it's a legal and ethical anomaly."
