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For years, assistance dogs have been used to detect low blood sugar levels in their diabetic owners and warn of an impending hypoglycemia attack. Scientists have finally figured out how dogs are able to accomplish this feat—an insight that could lead to new medical sensors.

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Dogs don’t so much see the world as they do smell it. Our canine companions can detect the tiniest odor concentrations—around one part per trillion. For us, that would be like detecting a teaspoon of sugar in two Olympic sized swimming pools. This allows them to work as medical detection dogs, where they sniff out various forms of cancer and diabetes.

Image: Medical Detection Dogs/Agenda Screening Services

In the case of diabetes, specially trained dogs can tell when their owner’s blood sugar level is low—a sign of a possible hypoglycemia attack. For people with type 1 diabetes, low blood sugar can cause problems like shakiness, disorientation, and fatigue. Failure to receive a sugar boost can lead to a seizure and even unconsciousness. For some, these episodes occur suddenly and with little warning. When a diabetes detection dog senses that their owner is in trouble, they notify them by performing a predetermined task, such as barking, laying down, or putting their paw on their shoulder.

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But how do these dogs know? What is it, exactly, that they’re sensing or smelling? This question has mystified scientists for years, but a new study by researchers from the Wellcome Trust-MRC Institute of Metabolic Science and the University of Cambridge has finally provided the answer.

It’s isoprene. That’s what these dogs are smelling—a common natural chemical found in human breath.

The scientists recruited eight women with type 1 diabetes, and under controlled conditions, lowered their blood sugar levels. Using mass spectrometry, they looked for specific chemical signatures to detect the presence of certain molecules. Looking at the data, the researchers found that isoprene rose significantly during hypoglycemia (the medical term for critically low blood sugar levels). In some cases, the presence of isoprene nearly doubled.

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Humans are oblivious to isoprene, but the researchers figure that dogs are particularly sensitive to the chemical, and can easily tell when their owner’s breath contains too much of it. As to why the body produces more isoprene during hypoglycemia, the researchers think it’s a byproduct of cholesterol production. Still, they’re not entirely sure why this chemical rises when blood sugar gets low.

Using this knowledge, the researchers would like to develop a medical sensor that does the same thing as diabetes sniffing dogs. What’s more, a handy breath device could replace the current finger prick test, which is inconvenient, painful, and relatively expensive.

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It’s important that we don’t overstate some of the purported abilities of medical detection dogs. They seem to be pretty good at detecting certain cancers (e.g. urological cancers and breast cancer) and diabetes, but many of these accounts are anecdotal, and much of the research tied to these canine abilities is still in early stages. Claims that dogs can sniff out lung cancer, colorectal cancer, and even Parkinson’s Disease are still under investigation and are far from proven.

Still, it’s an exciting line of medical research that, like this recent study, could lead to new scientific insights and powerful new medical technologies.

[Diabetes Care]