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Girl's drink-drive study helps breathe new life into science

DICK AHLSTROM, Science Editor

Fri, Jan 09, 2009

A YOUNG scientist from Co Kerry believes she has discovered a flaw in drink-driving breathalyser results.

Her research suggests that both diabetics and those on very low-calorie diets are more likely to show false positive results because of chemical changes in their blood.

Ciara Stein (13), who is a student at Presentation Secondary School in Tralee, explained how these devices could misread results and indicate a person was drink-driving.

“Diabetics and people on very, very low calorie diets can trigger false positives on breathalyser tests,” she said yesterday.

Ciara’s study is one of 500 currently on display at the RDS in the 2009 BT Young Scientist and Technology Exhibition. The overall young scientist of the year will be announced later this evening.

“This project has lots of importance to lawyers,” Ciara suggested.

The chemical changes in the blood are caused when levels of sugar drop too low, she explained.

“If you are diabetic or you are on a very low calorie diet, you can become hypoglycaemic – your blood sugar is too low. When this happens, you get ketones on your breath,” she said.

The simplest ketone is acetone. “If it starts to build up on your breath, it can become toxic.”

In response, the body changes the acetone into a form of alcohol, isopropanol. However, breathalysers cannot always distinguish between isopropanol and drinking alcohol, ethanol, she said. “They are very close to one another with the only thing one is primary [ethanol] and one secondary [isopropanol],” she said. Both acetone and isopropanol were common on the breaths of diabetics. “Type I diabetics would be most likely to have these on their breath,” Ciara said.

Her interest was sparked on reading a report about a teetotaller pilot from Sweden who was on a low-calorie diet and who used a breathalyser to check his breath periodically for alcohol. He found he registered almost 20 milligrams per millilitre of blood (20mg/ml), despite the fact he had not consumed any alcohol.

Real problems could arise if Ireland were to lower its blood alcohol level, currently 80mg/ml, she said. “If we reduce it to zero, we are doomed; if we reduce it to 50, we are in trouble,” she said.

A spokesman in the Garda Press Office said he was not aware of any potential problem with readings for diabetics and people on low-calorie diets. “It is certainly news to me,” he said last night. “That is the first time I have heard of it in relation to diabetics or low-calorie diets.”

It would be for a lawyer to raise the issue in court if it were to be used for a defence, but there had been no such cases, he said. “I presume it would have come to light before this,” he added.

© 2009 The Irish Times