San Diego DUI Lawyers and Attorneys Specializing in DUI Defense Since 1979

Effect of Body Temperature on Breathlyzer Tests

An article in 721 Michigan Bar Journal (September 1982), titled “Body Temperature and the Breathalyzer Boobytrap”, discussed the effects fluctuation in body temperature can have on breath-alcohol testing. The typical body temperature of a San Francisco DUI suspect is 37 degrees Celsius (98.6 degrees Fahrenheit). If the suspect is ill, however, their body temperature can rise up to 1.8 degrees F, 1 degree C. This increase might seem very small, yet it can affect the 1:2100 blood-to-alveolar air ratio used in DUI breath alcohol testing. This affect can increase the test result up to 7% higher.

The air sacs in your lungs, or the alveoli, are the location that the exchange of gases takes place between the blood and expired alveolar air.

“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.” (See “Breath Tests for Blood Alcohol Determination: Partition Ratio”)

- Srikumaran K. Melethil, Ph.D., Professor of Pharmacology at the University of Missouri, Kansas City

In other words, 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, the possibility of a 7% increase in breath-alcohol test results was originally communicated by Dr. Michael Hlastala of the University of Washington School of Medicine. According to Dr. Hlastala, 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 up to 1.8 degrees F (1 degree C) from the average value of 98.6 degrees F (37 degrees C). (“Physiological Errors Associated with Alcohol Breath Testing”, 9(6) The Champion 18.) Dr. Hlastala continued on to say, “the temperature of any individual may vary from time to time during the day” which comes to a 6.5% error for every 1.8 degrees F (1 degree C) difference from the average body temperature.

Humidity is another factor that can cause error in the test results. If your body temperature is above the average temperature, it could increase the humidity in your breath. This means: the more moisture in the breath, the high the concentration of alcohol in it. The affect here can, again, result in a falsely high test result.