Dogs are well known for their superior sense of smell, which is estimated to be at least a thousand times more sensitive than humans'.
But it's only in recent years that this skill has been honed for medical purposes, sniffing out dips in blood sugar in people with diabetes, and even detecting cancer before noticeable symptoms have developed; this is at the heart of the work of M edical Detection Dogs, a charity that trains pooches for this purpose.
It currently has 50 placed Medical Alert Assistance Dogs, of which 90 per cent are diabetes alert dogs, and is training 10 Cancer Detection Dogs.
Dr Claire Guest, the charity's chief executive, knows first-hand what lifesavers the dogs can be; her own Labrador, Daisy, alerted her to breast cancer.
Daisy was in training to sniff out prostate and bladder cancer at the time, when she started jumping up at Guest for no apparent reason and seemed unusually attentive and anxious. One day she bumped into Guest's chest with her nose and it was unusually sore, so she decided to have it checked out.
"I had a very deep breast cancer which wouldn't have been found for years without Daisy alerting me to it," says Guest, 50, who had a successful lumpectomy and radiotherapy after her 2009 diagnosis.
Her interest in dogs' cancer-sniffing abilities had actually been sparked years earlier, after a friend's pooch kept licking and sniffing a mole on her leg, which turned out to be malignant melanoma.
"From the description of the dog's behaviour, I was certain that it had smelt this change," says Guest.
Her theories were backed up by scientific studies. Dogs can detect minute odour alterations that occur during the very early stages of medical changes.
In 2008, the first diabetes alert dog was trained, and in the same year the Medical Detection Dogs charity was formed. It has just welcomed the Duchess of Cornwall as its patron.
As well as diabetes, Medical Alert Assistance Dogs are trained to help people with conditions including nut allergies, by alerting them when a nut allergen's present.
Canines are also being trained to help people with Addison's disease and narcolepsy, and it's hoped the list of conditions they can assist with will continue to grow in the future.
A large proportion of the Medical Detection Dogs are Labradors, which often have a very good sense of smell as well as a suitable temperament, but Spaniels, crossbreeds and even Yorkshire Terriers are also used.
The smell recognition training for Medical Alert Assistance Dogs can take just six weeks, and the dogs are then taught to alert their owner to problems, with signals such as nudges, licks, a push of the hand or even a simple stare. If the owner misses the signal, the dog will jump up, and get the blood testing or medical kit in their mouths and present it to them.
In contrast, Cancer Detection Dogs don't come into direct contact with their subjects, but screen samples from donors in a training area, and are taught which ones have the odour of cancer.
They're currently being trained to recognise cancers for which there is no reliable lab test, such as prostate, bladder or renal cancers. It's hoped that in the future they'll be able to detect ovarian and pancreatic cancers too.
The cancer detection work's still at the research and development stage but Guest has high hopes. Her dog Daisy, for example, has screened 7,000 bladder cancer urine samples, with 93 per cent accuracy.
"The indication is that a lot of 'invisible' cancers aren't invisible to dogs," she says.
The charity relies on fundraising and donations and gets no Government funding.
Guest says: "The dogs save the NHS a huge amount of money through stopping hospital admissions and reducing medical care, and it would be nice in the future if the dogs could at least be part-funded.
"These dogs enable people to retain their independence and they don't need carers. There are huge benefits, but it's still early days."
:: For more information visit medicaldetectiondogs.org.uk
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