Breathalyser tests are given by most law enforcement agencies to test drivers suspected of driving under the influence of alcohol. The accuracy of the results has sometimes been disputed in court by defence lawyers and the reliability of the testing has come under scrutiny. A number of substances and conditions not related to ingestion of alcoholic beverages may cause the breath alcohol to rate positive on the Breathalyzer scale.
The equipment tests for breath-alcohol content and not blood alcohol content (BAC) of the person being tested. A more accurate test would be a blood test, but Breathalyzers are used for their expedience and low cost. Most devices assume a ratio of 2,100 to 1 between BAC and breath alcohol content. Protocols call for the test to be administered under certain conditions in regard to time of test and environment of testing as well as maintenance of equipment and its use.
Breathalyser tests do not have a fine enough calibration to account for physical variations in human physique, such as metabolism, weight or height. The variety in physical types may change the ratio for a particular individual and make the 2,100 to 1 equation incorrect. Increased physical activity before a breath test is another factor proven to affect breath alcohol test results, decreasing BAC readings by as much as 25 per cent. There has been much speculation and some research into the ideas that test outcomes are affected by trace residue of alcohols in the mouth, ketone blood levels of diabetics, chemical fumes in the environment, recent physical exercise by test subject and ingestion of other substances.
Several factors may yield false positive results. Any of the following--the imperfect use of testing equipment, its improper maintenance or reliance on field testing, that is, testing at the roadside instead of in an environmentally controllable location, such as a police station--can affect the outcome.
Research is not conclusive about some often-mentioned possible causes of false positive readings. It is suspected that residue of alcohols can be in the soft tissue of the mouth or oesophagus from belching, acid reflux or using mouth wash. This residue will be picked up in the breath and can influence readings. Likewise fumes from paints, adhesives and plastics in the immediate environment may produce false positive Breathalyzer tests. Some have even suggested that radio frequencies and cell phone use can affect results.
The use of common asthma inhalers can cause breath alcohol tests to show positive, even when test subjects have not used alcohol. Diabetics undergoing breath alcohol testing may show levels indicating intoxication because the levels of ketones in their blood may be high enough to register on the Breathalyzer scale by showing high levels of acetone.
Newer models of testing equipment have corrected for some of these variables. Drivers can become aware of the possible variables affecting outcome of breath alcohol tests and be aware of their environment and physical condition at the time of testing. Law enforcement officers can become aware of the wild card variables. If they are using the latest equipment, false positive results can be avoided.