Susanne McCafferty, 44, had expected to be able to take her faithful companion Garner - nominated in this year's Guide Dog of the Year awards - with her to Aberdeen Royal Infirmary for an appointment - at which she was to be told that she was suffering from terminal cancer.
However, the patient-transport crew refused to allow the Labrador to go in the ambulance taking her from her home in the Aberdeenshire town of Peterhead to Aberdeen, wrongly claiming the dog required a special harness which could be bolted to the floor.
Mrs McCafferty - a former nurse who has been battling various forms of cancer since she was a teenager - had to spend six hours at the clinic without the companionship of her faithful guide dog when she was given the devastating news that her cancer had spread and was untreatable.
Mrs McCafferty, who has been registered blind since 2009, said last night: "It's disgusting.
"I was crying when they forced me to leave Garner at home.
"On the drive through to Aberdeen, they were telling me it was their policy not to take dogs in the ambulance.
"They said that if I'd told them that the dog was coming with me, they would have ordered a special harness to bolt him to the floor.
"I'd never heard anything like it. He's never needed a harness to travel before.
"You can even take guide dogs on a plane, so it doesn't make sense."
She added: "Garner is my eyes and he's just my rock. I can't go anywhere without him."
During her six-hour stay at the Aberdeen Royal Infirmary, Mrs McCafferty was unable to buy a cup of coffee or a sandwich because she could not move without the assistance of Garner.
She said: "By the time the patient-transport people came back to pick me up, I was very weak. I'd nothing to eat all day."
She added: "I'm a strong believer in euthanasia and there have been times when the pain has become so bad I've asked a friend to end it, to put a pillow over my face. But Garner is the reason I get up in the mornings."
Garner, who has been Mrs McCafferty's guide dog since March last year, has been nominated for an award in the life changing category in this year's UK Guide Dogs of the Year awards after he barked to alert a neighbour when Mrs McCafferty slipped in her shower.
A spokesman for the Scottish Ambulance Service confirmed last night that Mrs McCafferty should not have been told to leave her dog at home. He said "We will be writing to the patient concerned to apologise for any inconvenience caused and assure her that the appropriate steps have now been taken to make sure that this does not happen again and that her guide dog can accompany her in future."
Jane Horsburgh, the Guide Dogs' public policy manager, said: "Guide dog owners have the right to take their dogs with them in ambulances.. What was a simple enough request not being fulfilled falls short of adequate patient care."