Effect of Body Temperature on Breathalyzer Tests

In the September 1982 editions of the Michigan Bar Journal, An article entitled “Body Temperature and the Breathalyzer Booby-Trap”, discussed the factor of body temperature with regards to breath-alcohol testing. The common body temperature of a DUI suspect in San Francisco is approximately 37 degrees Celsius (98.6 degrees Fahrenheit). An illness can cause an increase by approximately 1 degree Celsius (1.8 degrees Fahrenheit). The increase may seem minimal, but it can greatly affect the 1:2100 blood-to-alveolar air ratios used by the breathalyzer. This affect can increase the test results up to 7%.

Air sacs in your lungs, known as alveoli, are the location where the exchange of gases between blood and expired alveolar air takes place.

A direct correlation is assumed between the concentration of alcohol in the alveolar air and concentration of alcohol in the blood, more precisely, ethanol. This assumption is based on Henry's Law, which states that, at constant temperature, the concentration of gas dissolved in a liquid is proportional to its concentration in the air directly above the liquid.
- Srikumaran K. Melethil, Ph.D., Professor of Pharmacology at the University of Missouri, Kansas City

Therefore, when finding your blood-alcohol content, the larger the concentration of alcohol in your blood, the larger the concentration will be in expired alveolar air.

In 1985, Dr. Michael Hlastala of the University of Washington School of Medicine first stated the possibility of a 7% increase in breath-alcohol test results. Based on Dr Hlastala’s findings, the partition ratio for alcohol in the blood is affected by the actual body temperature compared to the normal body temperature. A healthy individual may fluctuate 1 degree Celsius (1.8 degrees Fahrenheit) from the average of 37 degrees Celsius (98.6 degrees Fahrenheit). (Physiological Errors Associated with Alcohol Breath Testing, 9(6) The Champion 18.) Dr. Hlastala went on to say that the temperature of an individual may vary from time to time during the day, which comes to a 6.5% error for every 1 degree Celsius (1.8 degrees Fahrenheit) compared to that of the average body temperature.

Humidity is also a factor that may cause an error in breath alcohol test results. Should your body temperature be above the average body temperature, an increase in the humidity in your breath may occur. In other words, the more moisture in your breath, the larger the concentration of alcohol is in the breath. The affect here can also result in an inaccurate test result.

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