Many police departments in Texas and around the country use portable breath-testing devices to determine whether or not motorists have consumed alcohol. However, prosecutors do not generally rely on the results of roadside breath tests to establish impairment beyond a reasonable doubt, as the fuel-cell based devices issued to police officers are known to be unreliable in many situations.
Drivers who suffer from medical conditions including acid reflux disease and diabetes have been known to fail such tests despite consuming little or no alcohol, and there is evidence to suggest that individuals who follow strict ketogenic diets may also have good reason to be concerned when asked to blow into a portable breath testing device. Diets low in carbohydrates have become extremely popular in recent years because they prompt the body to deplete its glucose stores and go into a metabolic state known as ketosis. During ketosis, acetone is produced by the liver as it burns fat to provide the body with energy. Isopropyl alcohol is one of the byproducts of this process.
While even diets containing virtually no carbohydrates would be unlikely to cause a sober driver to fail a breath test, they could be enough to result in a DUI charge for motorists who consumed a small amount of alcohol before getting behind the wheel. Ketosis could also make it extremely difficult to start vehicles equipped with ignition interlock technology as the systems are designed to prevent driving when even trace amount of alcohol are detected.
There are situations where experienced criminal defense attorneys may question toxicology evidence provided by equipment considered far more reliable than the portable devices issued to police officers. The infrared spectroscopy machines found in most police stations require meticulous maintenance and regular recalibration, and even blood evidence may be questioned when a clear chain of custody cannot be established and samples may have been mishandled.