Friday, January 17, 2014

What Causes An Incorrect Positive To Have An Alcohol Test

Many substances besides alcohol can cause positive BAC test results

There are many ways to measure a person's blood-alcohol concentration, some of which are more accurate than others. Blood testing is the most accurate method to measure someone's BAC, but this is impractical in the field. Because of this, breath analyzer tests and urine tests are more common methods of BAC testing, but they are also less reliable. There are numerous ways to get false-positive readings using these methods.

Unreliable Testing Methods

Urine alcohol screen tests that measure levels of a metabolite of alcohol called ethyl glucuronide are unreliable because the test is too sensitive, according to the federal Substance Abuse and Mental Health Services Administration. EtG is reported to be detectable in the urine up to 80 hours after alcohol consumption. However, exposure to food or medicines that contain even low levels of alcohol can cause a positive EtG reading even when no alcohol has been consumed.


A study in the International Journal of Obesity in 2006 reported that an individual's diet can cause false-positive readings in breath analyzer tests for alcohol. Very low calorie diets, or other diets that cause the body to burn fat instead of carbohydrates as its primary source of energy, can cause increased levels of acetone in the blood. The extra acetone can be reduced by bodily processes into isopropanol which will cause false-positive breath test readings.

Environmental Factors

Various environmental factors can also contribute to false positive breath analyzer tests. Solvents and other compounds found in substances like paints, lacquers, gasoline and cleaning fluids can cause people who work with them to give false-positive breath test readings due to inhaling and subsequently exhaling the fumes. Certain foods, especially bread products, can cause false-positive readings if consumed within 15 minutes prior to taking a breath test. Some medications like asthma inhalers or nasal decongestants can also have this effect.

Physiology and Health

Like people on very low calorie diets, individuals with diabetes can sometimes have higher concentrations of acetone in their blood which may cause false-positive breath analyzer readings. Many breath analyzer machines work on the assumption that a person's hematocrit value (the cell volume of their blood) is 47 percent. However, hematocrit values can fall anywhere within a range of 37 to 52 percent, depending on the sex of the person being tested. Lower hematocrit values can cause falsely high breath test readings.

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