It's been known for some time that dogs can detect the onset of hypoglycaemia (low blood sugar) in the breath of type 1 diabetics – there are even helper dogs that are trained to do so. Now, scientists at the University of Cambridge believe that they may have figured out just what it is that those dogs are smelling. The discovery could potentially lead to a breathalyzer-like replacement for uncomfortable finger-prick tests.

In the study, the researchers gradually brought down the blood glucose levels of eight women in their forties, all type 1 diabetics. As they did so, they used a mass spectrometer to analyze chemicals in their breath.

They discovered that levels of the chemical isoprene – which is present in our breath normally, in small amounts – drastically increased at the onset of hypoglycaemia. Although it's suspected that isoprene is a byproduct of cholesterol production, it's still not clear why its levels should rise when glucose levels fall.

Nonetheless, it could be what the dogs are detecting.

"Humans aren't sensitive to the presence of isoprene, but dogs with their incredible sense of smell, find it easy to identify," says Cambridge's Dr. Mark Evans. "It provides a 'scent' that could help us develop new tests for detecting hypoglycaemia and reducing the risk of potentially life-threatening complications for patients living with diabetes. It's our vision that a new breath test could at least partly – but ideally completely – replace the current finger-prick test."

A paper on the research was recently published in the journal Diabetes Care.